CFVariable: CF data variable
In ncdfCF: Easy Access to NetCDF Files with CF Metadata Conventions
CFVariable R Documentation
CF data variable
Description
This class represents a CF data variable,
the object that provides access to an array of data.
The CF data variable instance provides access to all the details that have
been associated with the data variable, such as axis information, grid
mapping parameters, etc.
Super class
ncdfCF::CFObject -> CFVariable
Active bindings
friendlyClassName(read-only) A nice description of the class.
axes(read-only) List of instances of classes descending from
CFAxis that are the axes of the data object. If there are any scalar
axes, they are listed after the axes that associate with the dimensions
of the data. (In other words, axes 1..n describe the 1..n data
dimensions, while any axes n+1..m are scalar axes.)
crsThe coordinate reference system of this variable,
as an instance of CFGridMapping. If this field is NULL, the
horizontal component of the axes are in decimal degrees of longitude
and latitude.
cell_measures(read-only) List of the CFCellMeasure objects of
this variable, if defined.
dimids(read-only) Retrieve the dimension ids used by the
NC variable used by this variable.
dimnames(read-only) Retrieve dimnames of the data variable.
auxiliary_names(read-only) Retrieve the names of the auxiliary
longitude and latitude grids as a vector of two character strings, in
that order. If no auxiliary grids are defined, returns NULL.
gridLongLatRetrieve or set the grid of longitude and latitude
values of every grid cell when the main variable grid has a different
coordinate system.
crs_wkt2(read-only) Retrieve the coordinate reference system
description of the variable as a WKT2 string.
Methods
Public methods
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
Inherited methods
Method new()
Create an instance of this class.
Usage
CFVariable$new(
var,
axes,
values = values,
start = NA,
count = NA,
attributes = data.frame()
)
Arguments
varThe NCVariable instance upon which this CF variable is based
when read from a netCDF resource, or the name for the new CF variable
to be created.
axesList of instances of CFAxis to use with this variable.
valuesOptional. The values of the variable in an array.
startOptional. Vector of indices where to start reading data
along the dimensions of the array on file. The vector must be NA to
read all data, otherwise it must have agree with the dimensions of the
array on file. Ignored when argument var is not an NCVariable
instance.
countOptional. Vector of number of elements to read along each
dimension of the array on file. The vector must be NA to read to the
end of each dimension, otherwise its value must agree with the
corresponding start value and the dimension of the array on file.
Ignored when argument var is not an NCVariable instance.
attributesOptional. A data.frame with the attributes of the
object. When argument var is an NCVariable instance and this
argument is an empty data.frame (default), arguments will be read
from the resource.
Returns
A CFVariable instance.
Method print()
Print a summary of the data variable to the console.
Usage
CFVariable$print(...)
Arguments
...Arguments passed on to other functions. Of particular interest
is width = to indicate a maximum width of attribute columns.
Method brief()
Some details of the data variable.
Usage
CFVariable$brief()
Returns
A 1-row data.frame with some details of the data variable.
Method shard()
The information returned by this method is very concise
and most useful when combined with similar information from other
variables.
Usage
CFVariable$shard()
Returns
Character string with very basic variable information.
Method peek()
Retrieve interesting details of the data variable.
Usage
CFVariable$peek()
Returns
A 1-row data.frame with details of the data variable.
Method detach()
Detach the various properties of this variable from an
underlying netCDF resource.
Usage
CFVariable$detach()
Returns
Self, invisibly.
Method time()
Return the time object from the axis representing time.
Usage
CFVariable$time(want = "time")
Arguments
wantCharacter string with value "axis" or "time", indicating
what is to be returned.
Returns
If want = "axis" the CFAxisTime axis; if want = "time" the
CFTime instance of the axis, or NULL if the variable does not have a
"time" axis.
Method raw()
Retrieve the data in the object exactly as it was read from
a netCDF resource or produced by an operation.
Usage
CFVariable$raw()
Returns
An array, matrix or vector with (dim)names set.
Method array()
Retrieve the data in the object in the form of an R array,
with axis ordering Y-X-others and Y values going from the top down.
Usage
CFVariable$array()
Returns
An array or matrix of data in R ordering, or a vector if
the data has only a single dimension.
Method subset()
This method extracts a subset of values from the array of
the variable, with the range along each axis to extract expressed in
coordinate values of the domain of each axis.
Usage
CFVariable$subset(..., rightmost.closed = FALSE)
Arguments
...One or more arguments of the form axis = range. The "axis"
part should be the name of an axis or its orientation X, Y, Z or
T. The "range" part is a vector of values representing coordinates
along the axis where to extract data. Axis designators and names are
case-sensitive and can be specified in any order. If values for the
range per axis fall outside of the extent of the axis, the range is
clipped to the extent of the axis.
rightmost.closedSingle logical value to indicate if the upper
boundary of range in each axis should be included. You must use the
argument name when specifying this, like rightmost.closed = TRUE, to
avoid the argument being treated as an axis name.
Details
The range of values along each axis to be subset is expressed in
coordinates of the domain of the axis. Any axes for which no selection
is made in the ... argument are extracted in whole. Coordinates can
be specified in a variety of ways that are specific to the nature of
the axis. For numeric axes it should (resolve to) be a vector of real
values. A range (e.g. 100:200), a vector (c(23, 46, 3, 45, 17), a
sequence (seq(from = 78, to = 100, by = 2), all work. Note, however,
that only a single range is generated from the vector so these examples
resolve to (100, 200), (3, 46), and (78, 100), respectively. For
time axes a vector of character timestamps, POSIXct or Date values
must be specified. As with numeric values, only the two extreme values
in the vector will be used.
If the range of coordinate values for an axis in argument ... extends
the valid range of the axis, the extracted data will start at the
beginning for smaller values and extend to the end for larger values.
If the values envelope the valid range the entire axis will be
extracted in the result. If the range of coordinate values for any axis
are all either smaller or larger than the valid range of the axis then
nothing is extracted and NULL is returned.
The extracted data has the same dimensional structure as the data in
the variable, with degenerate dimensions dropped. The order of the axes
in argument ... does not reorder the axes in the result; use the
array() method for this.
As an example, to extract values of a variable for Australia for the
year 2020, where the first axis in x is the longitude, the second
axis is the latitude, both in degrees, and the third (and final) axis
is time, the values are extracted by x$subset(X = c(112, 154), Y = c(-9, -44), T = c("2020-01-01", "2021-01-01")). Note that this works
equally well for projected coordinate reference systems - the key is
that the specification in argument ... uses the same domain of values
as the respective axes in x use.
Auxiliary coordinate variables
A special case exists for variables where the horizontal dimensions (X
and Y) are not in longitude and latitude coordinates but in some other
coordinate system. In this case the netCDF resource may have so-called
auxiliary coordinate variables for longitude and latitude that are
two grids with the same dimension as the horizontal axes of the data
variable where each pixel gives the corresponding value for the
longitude and latitude. If the variable has such auxiliary coordinate
variables then you can specify their names (instead of specifying the
names of the primary planar axes). The resolution of the grid that is
produced by this method is automatically calculated. If you want to
subset those axes then specify values in decimal degrees; if you want
to extract the full extent, specify NA for both axes.
Returns
A CFVariable instance, having the axes and attributes of the
variable, or NULL if one or more of the selectors in the ...
argument fall entirely outside of the range of the axis. Note that
degenerate dimensions (having length(.) == 1) are dropped from the
data array but the corresponding axis is maintained in the result as a
scalar axis.
If self is linked to a netCDF resource then the result will be linked
to the same netCDF resource as well, except when auxiliary coordinate
variables have been selected for the planar axes.
Method summarise()
Summarise the temporal domain of the data, if present, to a
lower resolution, using a user-supplied aggregation function.
Attributes are copied from the input data variable or data array. Note
that after a summarisation the attributes may no longer be accurate.
This method tries to sanitise attributes but the onus is on the calling
code (or yourself as interactive coder). Attributes like
standard_name and cell_methods likely require an update in the
output of this method, but the appropriate new values are not known to
this method. Use CFVariable$set_attribute() on the result of this
method to set or update attributes as appropriate.
Usage
CFVariable$summarise(name, fun, period, era = NULL, ...)
Arguments
nameCharacter vector with a name for each of the results that
fun returns. So if fun has 2 return values, this should be a vector
of length 2. Any missing values are assigned a default name of
"result_#" (with '#' being replaced with an ordinal number).
funA function or a symbol or character string naming a function
that will be applied to each grouping of data. The function must return
an atomic value (such as sum() or mean()), or a vector of atomic
values (such as range()). Lists and other objects are not allowed and
will throw an error that may be cryptic as there is no way that this
method can assert that fun behaves properly so an error will pop up
somewhere, most probably in unexpected ways. The function may also be
user-defined so you could write a wrapper around a function like lm()
to return values like the intercept or any coefficients from the object
returned by calling that function.
periodThe period to summarise to. Must be one of either "day",
"dekad", "month", "quarter", "season", "year". A "quarter" is the
standard calendar quarter such as January-March, April-June, etc. A
"season" is a meteorological season, such as December-February,
March-May, etc. (any December data is from the year preceding the
January data). The period must be of lower resolution than the
resolution of the time axis.
eraOptional, integer vector of years to summarise over by the
specified period. The extreme values of the years will be used. This
can also be a list of multiple such vectors. The elements in the list,
if used, should have names as these will be used to label the results.
...Additional parameters passed on to fun.
Returns
A CFVariable object, or a list thereof with as many
CFVariable objects as fun returns values.
Method profile()
This method extracts profiles of values from the array of
the variable, with the location along each axis to extract expressed in
coordinate values of each axis.
Usage
CFVariable$profile(..., .names = NULL, .as_table = FALSE)
Arguments
...One or more arguments of the form axis = location. The
"axis" part should be the name of an axis or its orientation X, Y,
Z or T. The "location" part is a vector of values representing
coordinates along the axis where to profile. A profile will be
generated for each of the elements of the "location" vectors in all
arguments.
.namesA character vector with names for the results. The names
will be used for the resulting CFVariable instances, or as values for
the "location" column of the data.table if argument .as_table is
TRUE. If the vector is shorter than the longest vector of locations
in the ... argument, a name "location_#" will be used, with the #
replaced by the ordinal number of the vector element.
.as_tableLogical to flag if the results should be CFVariable
instances (FALSE, default) or a single data.table (TRUE). If
TRUE, all ... arguments must have the same number of elements, use
the same axes and the data.table package must be installed.
Details
The coordinates along each axis to be sampled are expressed in
values of the domain of the axis. Any axes which are not passed as
arguments are extracted in whole to the result. If bounds are set on
the axis, the coordinate whose bounds envelop the requested coordinate
is selected. Otherwise, the coordinate along the axis closest to the
supplied value will be used. If the value for a specified axis falls
outside the valid range of that axis, NULL is returned.
A typical case is to extract the temporal profile as a 1D array for a
given location. In this case, use arguments for the latitude and
longitude on an X-Y-T data variable: profile(lat = -24, lon = 3).
Other profiling options are also possible, such as a 2D zonal
atmospheric profile at a given longitude for an X-Y-Z data variable:
profile(lon = 34).
Multiple profiles can be extracted in one call by supplying vectors for
the indicated axes: profile(lat = c(-24, -23, -2), lon = c(5, 5, 6)).
The vectors need not have the same length, unless .as_table = TRUE.
With unequal length vectors the result will be a list of CFVariable
instances with different dimensionality and/or different axes.
Auxiliary coordinate variables
A special case exists for variables where the horizontal dimensions (X
and Y) are not in longitude and latitude coordinates but in some other
coordinate system. In this case the netCDF resource may have so-called
auxiliary coordinate variables. If the variable has such auxiliary coordinate
variables then you can specify their names (instead of specifying the
names of the primary planar axes).
Returns
If .as_table = FALSE, a CFVariable instance, or a list
thereof with each having one profile for each of the elements in the
"location" vectors of argument ... and named with the respective
.names value. If .as_table = TRUE, a data.table with a row for
each element along all profiles, with a ".variable" column using the
values from the .names argument.
Method append()
Append the data from another CFVariable instance to the
current instance, along one of the axes. The operation will only
succeed if the axes other than the one to append along have the same
coordinates and the coordinates of the axis to append along have to be
monotonically increasing or decreasing after appending.
Usage
CFVariable$append(from, along)
Arguments
fromThe CFVariable instance to append to this data variable.
alongThe name of the axis to append along. This must be a single
character string and the named axis has to be present both in this data
variable and in the CFVariable instance in argument from.
Returns
self, invisibly, with the arrays from this data variable and
from appended.
Method terra()
Convert the data to a terra::SpatRaster (3D) or a
terra::SpatRasterDataset (4D) object. The data will be oriented to
North-up. The 3rd dimension in the data will become layers in the
resulting SpatRaster, any 4th dimension the data sets. The terra
package needs to be installed for this method to work.
Usage
CFVariable$terra()
Returns
A terra::SpatRaster or terra::SpatRasterDataset instance.
Method data.table()
Retrieve the data variable in the object in the form of a
data.table. The data.table package needs to be installed for this
method to work.
The attributes associated with this data variable will be mostly lost.
If present, attributes 'long_name' and 'units' are attached to the
data.table as attributes, but all others are lost.
Usage
CFVariable$data.table(var_as_column = FALSE)
Arguments
var_as_columnLogical to flag if the name of the variable should
become a column (TRUE) or be used as the name of the column with the
data values (FALSE, default). Including the name of the variable as a
column is useful when multiple data.tables are merged into one.
Returns
A data.table with all data points in individual rows. All axes
will become columns. Two attributes are added: name indicates the
long name of this data variable, units indicates the physical unit of
the data values.
Method is_coincident()
Tests if the other object is coincident with this data
variable: identical axes.
Usage
CFVariable$is_coincident(other)
Arguments
otherA CFVariable instance to compare to this data variable.
Returns
TRUE if the data variables are coincident, FALSE otherwise.
Method add_cell_measure()
Add a cell measure variable to this variable.
Usage
CFVariable$add_cell_measure(cm)
Arguments
cmAn instance of CFCellMeasure.
Returns
Self, invisibly.
Method add_auxiliary_coordinate()
Add an auxiliary coordinate to the appropriate axis of this
variable. The length of the axis must be the same as the length of the
auxiliary labels.
Usage
CFVariable$add_auxiliary_coordinate(aux, axis)
Arguments
auxAn instance of CFLabel or CFAxis.
axisAn instance of CFAxis that these auxiliary coordinates are
for.
Returns
Self, invisibly.
Method save()
Save the data object to a netCDF file.
Usage
CFVariable$save(fn, pack = FALSE)
Arguments
fnThe name of the netCDF file to create.
packLogical to indicate if the data should be packed. Packing is
only useful for numeric data; packing is not performed on integer values.
Packing is always to the "NC_SHORT" data type, i.e. 16-bits per value.
Returns
Self, invisibly.
Method clone()
The objects of this class are cloneable with this method.
Usage
CFVariable$clone(deep = FALSE)
Arguments
deepWhether to make a deep clone.
ncdfCF documentation built on Sept. 13, 2025, 5:07 p.m.
R Package Documentation
Browse R Packages
We want your feedback!
Note that we can't provide technical support on individual packages. You should contact the package authors for that.
| CFVariable | R Documentation |
CF data variable
Description
This class represents a CF data variable, the object that provides access to an array of data.
The CF data variable instance provides access to all the details that have been associated with the data variable, such as axis information, grid mapping parameters, etc.
Super class
ncdfCF::CFObject -> CFVariable
Active bindings
friendlyClassName(read-only) A nice description of the class.
axes(read-only) List of instances of classes descending from CFAxis that are the axes of the data object. If there are any scalar axes, they are listed after the axes that associate with the dimensions of the data. (In other words, axes
1..ndescribe the1..ndata dimensions, while any axesn+1..mare scalar axes.)crsThe coordinate reference system of this variable, as an instance of CFGridMapping. If this field is
NULL, the horizontal component of the axes are in decimal degrees of longitude and latitude.cell_measures(read-only) List of the CFCellMeasure objects of this variable, if defined.
dimids(read-only) Retrieve the dimension ids used by the NC variable used by this variable.
dimnames(read-only) Retrieve dimnames of the data variable.
auxiliary_names(read-only) Retrieve the names of the auxiliary longitude and latitude grids as a vector of two character strings, in that order. If no auxiliary grids are defined, returns
NULL.gridLongLatRetrieve or set the grid of longitude and latitude values of every grid cell when the main variable grid has a different coordinate system.
crs_wkt2(read-only) Retrieve the coordinate reference system description of the variable as a WKT2 string.
Methods
Public methods
Inherited methods
Method new()
Create an instance of this class.
Usage
CFVariable$new( var, axes, values = values, start = NA, count = NA, attributes = data.frame() )
Arguments
varThe NCVariable instance upon which this CF variable is based when read from a netCDF resource, or the name for the new CF variable to be created.
axesList of instances of CFAxis to use with this variable.
valuesOptional. The values of the variable in an array.
startOptional. Vector of indices where to start reading data along the dimensions of the array on file. The vector must be
NAto read all data, otherwise it must have agree with the dimensions of the array on file. Ignored when argumentvaris not anNCVariableinstance.countOptional. Vector of number of elements to read along each dimension of the array on file. The vector must be
NAto read to the end of each dimension, otherwise its value must agree with the correspondingstartvalue and the dimension of the array on file. Ignored when argumentvaris not anNCVariableinstance.attributesOptional. A
data.framewith the attributes of the object. When argumentvaris anNCVariableinstance and this argument is an emptydata.frame(default), arguments will be read from the resource.
Returns
A CFVariable instance.
Method print()
Print a summary of the data variable to the console.
Usage
CFVariable$print(...)
Arguments
...Arguments passed on to other functions. Of particular interest is
width = to indicate a maximum width of attribute columns.
Method brief()
Some details of the data variable.
Usage
CFVariable$brief()
Returns
A 1-row data.frame with some details of the data variable.
Method shard()
The information returned by this method is very concise and most useful when combined with similar information from other variables.
Usage
CFVariable$shard()
Returns
Character string with very basic variable information.
Method peek()
Retrieve interesting details of the data variable.
Usage
CFVariable$peek()
Returns
A 1-row data.frame with details of the data variable.
Method detach()
Detach the various properties of this variable from an underlying netCDF resource.
Usage
CFVariable$detach()
Returns
Self, invisibly.
Method time()
Return the time object from the axis representing time.
Usage
CFVariable$time(want = "time")
Arguments
wantCharacter string with value "axis" or "time", indicating what is to be returned.
Returns
If want = "axis" the CFAxisTime axis; if want = "time" the
CFTime instance of the axis, or NULL if the variable does not have a
"time" axis.
Method raw()
Retrieve the data in the object exactly as it was read from a netCDF resource or produced by an operation.
Usage
CFVariable$raw()
Returns
An array, matrix or vector with (dim)names set.
Method array()
Retrieve the data in the object in the form of an R array, with axis ordering Y-X-others and Y values going from the top down.
Usage
CFVariable$array()
Returns
An array or matrix of data in R ordering, or a vector if
the data has only a single dimension.
Method subset()
This method extracts a subset of values from the array of the variable, with the range along each axis to extract expressed in coordinate values of the domain of each axis.
Usage
CFVariable$subset(..., rightmost.closed = FALSE)
Arguments
...One or more arguments of the form
axis = range. The "axis" part should be the name of an axis or its orientationX,Y,ZorT. The "range" part is a vector of values representing coordinates along the axis where to extract data. Axis designators and names are case-sensitive and can be specified in any order. If values for the range per axis fall outside of the extent of the axis, the range is clipped to the extent of the axis.rightmost.closedSingle logical value to indicate if the upper boundary of range in each axis should be included. You must use the argument name when specifying this, like
rightmost.closed = TRUE, to avoid the argument being treated as an axis name.
Details
The range of values along each axis to be subset is expressed in
coordinates of the domain of the axis. Any axes for which no selection
is made in the ... argument are extracted in whole. Coordinates can
be specified in a variety of ways that are specific to the nature of
the axis. For numeric axes it should (resolve to) be a vector of real
values. A range (e.g. 100:200), a vector (c(23, 46, 3, 45, 17), a
sequence (seq(from = 78, to = 100, by = 2), all work. Note, however,
that only a single range is generated from the vector so these examples
resolve to (100, 200), (3, 46), and (78, 100), respectively. For
time axes a vector of character timestamps, POSIXct or Date values
must be specified. As with numeric values, only the two extreme values
in the vector will be used.
If the range of coordinate values for an axis in argument ... extends
the valid range of the axis, the extracted data will start at the
beginning for smaller values and extend to the end for larger values.
If the values envelope the valid range the entire axis will be
extracted in the result. If the range of coordinate values for any axis
are all either smaller or larger than the valid range of the axis then
nothing is extracted and NULL is returned.
The extracted data has the same dimensional structure as the data in
the variable, with degenerate dimensions dropped. The order of the axes
in argument ... does not reorder the axes in the result; use the
array() method for this.
As an example, to extract values of a variable for Australia for the
year 2020, where the first axis in x is the longitude, the second
axis is the latitude, both in degrees, and the third (and final) axis
is time, the values are extracted by x$subset(X = c(112, 154), Y = c(-9, -44), T = c("2020-01-01", "2021-01-01")). Note that this works
equally well for projected coordinate reference systems - the key is
that the specification in argument ... uses the same domain of values
as the respective axes in x use.
Auxiliary coordinate variables
A special case exists for variables where the horizontal dimensions (X
and Y) are not in longitude and latitude coordinates but in some other
coordinate system. In this case the netCDF resource may have so-called
auxiliary coordinate variables for longitude and latitude that are
two grids with the same dimension as the horizontal axes of the data
variable where each pixel gives the corresponding value for the
longitude and latitude. If the variable has such auxiliary coordinate
variables then you can specify their names (instead of specifying the
names of the primary planar axes). The resolution of the grid that is
produced by this method is automatically calculated. If you want to
subset those axes then specify values in decimal degrees; if you want
to extract the full extent, specify NA for both axes.
Returns
A CFVariable instance, having the axes and attributes of the
variable, or NULL if one or more of the selectors in the ...
argument fall entirely outside of the range of the axis. Note that
degenerate dimensions (having length(.) == 1) are dropped from the
data array but the corresponding axis is maintained in the result as a
scalar axis.
If self is linked to a netCDF resource then the result will be linked
to the same netCDF resource as well, except when auxiliary coordinate
variables have been selected for the planar axes.
Method summarise()
Summarise the temporal domain of the data, if present, to a lower resolution, using a user-supplied aggregation function.
Attributes are copied from the input data variable or data array. Note
that after a summarisation the attributes may no longer be accurate.
This method tries to sanitise attributes but the onus is on the calling
code (or yourself as interactive coder). Attributes like
standard_name and cell_methods likely require an update in the
output of this method, but the appropriate new values are not known to
this method. Use CFVariable$set_attribute() on the result of this
method to set or update attributes as appropriate.
Usage
CFVariable$summarise(name, fun, period, era = NULL, ...)
Arguments
nameCharacter vector with a name for each of the results that
funreturns. So iffunhas 2 return values, this should be a vector of length 2. Any missing values are assigned a default name of "result_#" (with '#' being replaced with an ordinal number).funA function or a symbol or character string naming a function that will be applied to each grouping of data. The function must return an atomic value (such as
sum()ormean()), or a vector of atomic values (such asrange()). Lists and other objects are not allowed and will throw an error that may be cryptic as there is no way that this method can assert thatfunbehaves properly so an error will pop up somewhere, most probably in unexpected ways. The function may also be user-defined so you could write a wrapper around a function likelm()to return values like the intercept or any coefficients from the object returned by calling that function.periodThe period to summarise to. Must be one of either "day", "dekad", "month", "quarter", "season", "year". A "quarter" is the standard calendar quarter such as January-March, April-June, etc. A "season" is a meteorological season, such as December-February, March-May, etc. (any December data is from the year preceding the January data). The period must be of lower resolution than the resolution of the time axis.
eraOptional, integer vector of years to summarise over by the specified
period. The extreme values of the years will be used. This can also be a list of multiple such vectors. The elements in the list, if used, should have names as these will be used to label the results....Additional parameters passed on to
fun.
Returns
A CFVariable object, or a list thereof with as many
CFVariable objects as fun returns values.
Method profile()
This method extracts profiles of values from the array of the variable, with the location along each axis to extract expressed in coordinate values of each axis.
Usage
CFVariable$profile(..., .names = NULL, .as_table = FALSE)
Arguments
...One or more arguments of the form
axis = location. The "axis" part should be the name of an axis or its orientationX,Y,ZorT. The "location" part is a vector of values representing coordinates along the axis where to profile. A profile will be generated for each of the elements of the "location" vectors in all arguments..namesA character vector with names for the results. The names will be used for the resulting
CFVariableinstances, or as values for the "location" column of thedata.tableif argument.as_tableisTRUE. If the vector is shorter than the longest vector of locations in the...argument, a name "location_#" will be used, with the # replaced by the ordinal number of the vector element..as_tableLogical to flag if the results should be
CFVariableinstances (FALSE, default) or a singledata.table(TRUE). IfTRUE, all...arguments must have the same number of elements, use the same axes and thedata.tablepackage must be installed.
Details
The coordinates along each axis to be sampled are expressed in
values of the domain of the axis. Any axes which are not passed as
arguments are extracted in whole to the result. If bounds are set on
the axis, the coordinate whose bounds envelop the requested coordinate
is selected. Otherwise, the coordinate along the axis closest to the
supplied value will be used. If the value for a specified axis falls
outside the valid range of that axis, NULL is returned.
A typical case is to extract the temporal profile as a 1D array for a
given location. In this case, use arguments for the latitude and
longitude on an X-Y-T data variable: profile(lat = -24, lon = 3).
Other profiling options are also possible, such as a 2D zonal
atmospheric profile at a given longitude for an X-Y-Z data variable:
profile(lon = 34).
Multiple profiles can be extracted in one call by supplying vectors for
the indicated axes: profile(lat = c(-24, -23, -2), lon = c(5, 5, 6)).
The vectors need not have the same length, unless .as_table = TRUE.
With unequal length vectors the result will be a list of CFVariable
instances with different dimensionality and/or different axes.
Auxiliary coordinate variables
A special case exists for variables where the horizontal dimensions (X and Y) are not in longitude and latitude coordinates but in some other coordinate system. In this case the netCDF resource may have so-called auxiliary coordinate variables. If the variable has such auxiliary coordinate variables then you can specify their names (instead of specifying the names of the primary planar axes).
Returns
If .as_table = FALSE, a CFVariable instance, or a list
thereof with each having one profile for each of the elements in the
"location" vectors of argument ... and named with the respective
.names value. If .as_table = TRUE, a data.table with a row for
each element along all profiles, with a ".variable" column using the
values from the .names argument.
Method append()
Append the data from another CFVariable instance to the
current instance, along one of the axes. The operation will only
succeed if the axes other than the one to append along have the same
coordinates and the coordinates of the axis to append along have to be
monotonically increasing or decreasing after appending.
Usage
CFVariable$append(from, along)
Arguments
fromThe
CFVariableinstance to append to this data variable.alongThe name of the axis to append along. This must be a single character string and the named axis has to be present both in this data variable and in the
CFVariableinstance in argumentfrom.
Returns
self, invisibly, with the arrays from this data variable and
from appended.
Method terra()
Convert the data to a terra::SpatRaster (3D) or a
terra::SpatRasterDataset (4D) object. The data will be oriented to
North-up. The 3rd dimension in the data will become layers in the
resulting SpatRaster, any 4th dimension the data sets. The terra
package needs to be installed for this method to work.
Usage
CFVariable$terra()
Returns
A terra::SpatRaster or terra::SpatRasterDataset instance.
Method data.table()
Retrieve the data variable in the object in the form of a
data.table. The data.table package needs to be installed for this
method to work.
The attributes associated with this data variable will be mostly lost.
If present, attributes 'long_name' and 'units' are attached to the
data.table as attributes, but all others are lost.
Usage
CFVariable$data.table(var_as_column = FALSE)
Arguments
var_as_columnLogical to flag if the name of the variable should become a column (
TRUE) or be used as the name of the column with the data values (FALSE, default). Including the name of the variable as a column is useful when multipledata.tables are merged into one.
Returns
A data.table with all data points in individual rows. All axes
will become columns. Two attributes are added: name indicates the
long name of this data variable, units indicates the physical unit of
the data values.
Method is_coincident()
Tests if the other object is coincident with this data
variable: identical axes.
Usage
CFVariable$is_coincident(other)
Arguments
otherA
CFVariableinstance to compare to this data variable.
Returns
TRUE if the data variables are coincident, FALSE otherwise.
Method add_cell_measure()
Add a cell measure variable to this variable.
Usage
CFVariable$add_cell_measure(cm)
Arguments
cmAn instance of CFCellMeasure.
Returns
Self, invisibly.
Method add_auxiliary_coordinate()
Add an auxiliary coordinate to the appropriate axis of this variable. The length of the axis must be the same as the length of the auxiliary labels.
Usage
CFVariable$add_auxiliary_coordinate(aux, axis)
Arguments
auxAn instance of CFLabel or CFAxis.
axisAn instance of
CFAxisthat these auxiliary coordinates are for.
Returns
Self, invisibly.
Method save()
Save the data object to a netCDF file.
Usage
CFVariable$save(fn, pack = FALSE)
Arguments
fnThe name of the netCDF file to create.
packLogical to indicate if the data should be packed. Packing is only useful for numeric data; packing is not performed on integer values. Packing is always to the "NC_SHORT" data type, i.e. 16-bits per value.
Returns
Self, invisibly.
Method clone()
The objects of this class are cloneable with this method.
Usage
CFVariable$clone(deep = FALSE)
Arguments
deepWhether to make a deep clone.
R Package Documentation
Browse R Packages
We want your feedback!
Note that we can't provide technical support on individual packages. You should contact the package authors for that.
Embedding an R snippet on your website
Add the following code to your website.
For more information on customizing the embed code, read Embedding Snippets.