Coord: Coords
In hadley/ggplot2: Create Elegant Data Visualisations Using the Grammar of Graphics
Coord R Documentation
Coords
Description
All coord_*() functions (like coord_transform()) return a Coord* object
(like CoordTransform). These objects contain methods that support the
coordinate systems in ggplot2.
Details
Each of the Coord* objects is a ggproto() object, descended from the
top-level Coord, and each implements various methods and fields.
The object and its parameters are chaperoned by the Layout class.
To create a new type of Coord object, it is recommended
to extend not the base Coord class, but one of its children like
CoordCartesian.
When overriding the transform() method, it may be necessary to adapt the
implementation of render_bg() and possibly axis placement too.
An important data structure that coordinate systems create is the
panel_params structure. When overriding that structure, many methods may
need to be adapted as well.
Fields
defaultScaler boolean indicating whether this is the default
coordinate system. Non-default coordinate systems raise a message when
a new system replaces it.
clipA scalar string grid setting controlling whether layers should
be clipped to the extent of the plot panel extent. Can be "on" to
perform clipping, "off" to not clip, or "inherit" to take on the
setting of the parent viewport.
reverseA scalar string giving which directions to reverse. For
Cartesian systems, can be "none, "x", "y" or "xy" for both.
Non-Cartesian may define their own settings.
setup_paramsDescription
A function method for modifying or checking the parameters based on the
data. The default method parses the expand parameter.
Usage
Coord$setup_params(data)
Arguments
dataA list of data frames. The first item is the global data,
which is followed by layer data in subsequent items.
Value
A list of parameters
setup_dataDescription
A function method for modifying or checking the data prior to adding
defaults. The default method returns data unaltered.
Usage
Coord$setup_data(data, params)
Arguments
dataA list of data frames. The first item is the global data,
which is followed by layer data in subsequent items.
paramsA list of parameters coming from the setup_params()
method.
Value
A list of data frames of the same length as the data argument
setup_layoutDescription
A function method that acts as a hook for the coordinate system to have
input on the layout computed by facets.
Usage
Coord$setup_layout(layout, params)
Arguments
layoutA data frame computed by Facet$compute_layout().
Typically contains the faceting variables, ROW, COL, PANEL,
SCALE_X and SCALE_Y variables.
paramsA list of parameters coming from the setup_params()
method.
Value
A data frame from the modified layout argument. The default creates a
new COORD column to identify unique combinations of x and y scales for
efficiency purposes. It should never remove columns.
modify_scalesDescription
A function method for modifying scales in place. This is optional and
currently used by CoordFlip and CoordPolar to ensure axis positions are
conforming to the coordinate system.
Usage
Coord$modify_scales(scales_x, scales_y)
Arguments
scales_x,scales_yA list of trained scales for the x and y
aesthetics respectively.
Value
Nothing, this is called for the side effect of modifying scales.
setup_panel_paramsDescription
This function method is used to setup panel parameters per panel.
For efficiency reasons, this method is called once per combination of
x and y scales. It is used to instantiate ViewScale class objects and
ranges for position aesthetics and optionally append additional
parameters needed for the transform() method and rendering axes.
Usage
Coord$setup_panel_params(scale_x, scale_y, params)
Arguments
scale_x,scale_yA list of trained scales for the x and y
aesthetics respectively.
paramsA list of parameters coming from the setup_params()
method.
Value
A named list of view scales, ranges and other optional parameters.
setup_panel_guidesDescription
This function method is used to initiate position guides for each panel.
For efficiency reasons, this method is called once per combination of x
and y scales. For the primary and secondary positions, it should resolve
guides coming from the plot$guides field and Scale$guide fields and
set appropriate Guide$params$position parameters.
Usage
Coord$setup_panel_guides(panel_params, guides, params)
Arguments
panel_paramsA list of ViewScale class objects and additional
parameters from the setup_panel_params() method.
guidesA <Guides> ggproto class.
paramsA list of parameters coming from the setup_params()
method.
Value
The panel_params object but with a Guides class object appended with
the name 'guides'.
setup_panel_guidesDescription
This function method is used to train and transform position guides for each
panel. For efficiency reasons, this method is called once per combination
of x and y scales.
Usage
Coord$train_panel_guides(panel_params, layers, params)
Arguments
panel_paramsA list of ViewScale class objects, a Guides class
object and additional parameters from the setup_panel_params() method.
layersA list of layers from plot$layers.
paramsA list of parameters coming from the setup_params()
method.
Value
The panel_params object, but with trained and transformed guides
parameter.
transformDescription
This function method is used to apply transformations and rescale position
aesthetics. This method is used in several places:
The Geom drawing code, used through coord_munch() in many Geoms.
The Guide transform method
Panel grid transformation in render_bg()
Usage
Coord$transform(data, panel_params)
Arguments
dataA data frame with columns for numeric position aesthetics.
panel_paramsA list of ViewScale class objects and additional
parameters from the setup_panel_params() method.
Value
The data argument with rescaled and transformed position aesthetics.
distanceDescription
This function method is used to calculate distances between subsequent
data points. coord_munch() uses this method determine how many points
should be used to interpolate.
Usage
Coord$distance(x, y, panel_params)
Arguments
x,yx and y coordinates of a set of points in data space.
panel_paramsA list of ViewScale class objects and additional
parameters from the setup_panel_params() method.
Value
The data argument with rescaled and transformed position aesthetics.
backtransform_rangeDescription
This function method is used to convert ranges from transformed coordinates
back into data coordinates. The data coordinates may possibly be scale-
transformed. It is used in coord_munch() to ensure limits are in data
coordinates.
The back-transformation may be needed for coords such as coord_transform(),
where the range in the transformed coordinates differs from the range in
the untransformed coordinates.
Usage
Coord$backtransform_range(panel_params)
Arguments
panel_paramsA list of ViewScale class objects and additional
parameters from the setup_panel_params() method.
Value
A list containing numeric ranges for x and y in data coordinates.
rangeDescription
This function method is a small helper method to extract ranges from the
panel_params object. It exists because panel_params can be opaque at
times.
Usage
Coord$range(panel_params)
Arguments
panel_paramsA list of ViewScale class objects and additional
parameters from the setup_panel_params() method.
Value
A list containing numeric ranges for x and y.
draw_panelDescription
This function method is used to orchestrate decorating panel drawings with
foreground and background drawings. It is called once per panel, invokes
the render_fg() and render_bg() methods and enforces the clip field.
Usage
Coord$draw_panel(panel, params, theme)
Arguments
panelA grob containing drawn layers and facet foreground and
background.
paramsA list of ViewScale class objects and additional
parameters from the setup_panel_params() method.
themeA complete theme
Value
A grob with panel content.
render_fgDescription
This function method is used to draw the panel foreground. For all
intents and purposes is just the panel.border theme element, but you can
repurpose this method.
Usage
Coord$render_fg(panel_params, theme)
Arguments
panel_paramsA list of ViewScale class objects and additional
parameters from the setup_panel_params() method.
themeA complete theme
Value
A grob with panel foreground.
render_bgDescription
This function method is used to draw the panel background. Typically
this is a combination of the panel.background and panel.grid theme
elements.
Usage
Coord$render_bg(panel_params, theme)
Arguments
panel_paramsA list of ViewScale class objects and additional
parameters from the setup_panel_params() method.
themeA complete theme
Value
A grob with panel background.
labelsDescription
This function method is used to format axis titles. It is used in some
coordinate systems to (conditionally) swap x and y labels.
Usage
Coord$labels(labels, panel_params)
Arguments
labelsA named list containing an x list and a y list. The
x and y lists have primary and secondary labels.
panel_paramsA list of ViewScale class objects and additional
parameters from the setup_panel_params() method.
Value
A list with the same structure and names as the labels argument.
aspectDescription
This function method that gives the aspect ratio for panels. It allows for
CoordFixed to compute an aspect ratio based on data ranges.
Usage
Coord$render_bg(panel_params, theme)
Arguments
rangesA list of ViewScale class objects and additional
parameters from the setup_panel_params() method. If there are
multiple panels, the parameters for the first panel is used.
Value
A scalar numeric
render_axis_h,render_axis_vDescription
These function methods are used to render axes to place at the outside edge
of panels. Interior axes should not be rendered here. The render_axis_h()
methods produces the horizontal axes for the top and bottom position.
The render_axis_v() method renders the vertical axes for the left and
right position.
Usage
Coord$render_axis_h(panel_params, theme
Coord$render_axis_v(panel_params, theme)
Arguments
panel_paramsA list of ViewScale class objects, a Guides class
object and additional parameters from the setup_panel_params() method.
themeA complete theme
Value
For render_axis_h() a named list where "top" and "bottom" are grobs
with an axis. For render_axis_v() a named list where "left" and
"right" are grobs with an axis. These grobs should be zeroGrob()
when no axes should be rendered.
is_linearDescription
This function method is used to signal whether a coordinate system is
linear. In coord_munch() and several Geom drawing methods, it is used to
determine whether points should be interpolated.
Usage
Coord$is_linear()
Value
A scalar boolean.
is_freeDescription
This function method is used to signal whether a coordinate system supports
free scaling of axes in faceted plots. This should generally return FALSE
for coordinate systems that enforce a fixed aspect ratio.
Usage
Coord$is_free()
Value
A scalar boolean.
Conventions
The object name that a new class is assigned to is typically the same as the
class name. Coord class names are in UpperCamelCase and start with the
Coord* prefix, like CoordNew.
A constructor function is usually paired with a Coord class. The constructor
copies the coord class and populates parameters. The constructor function name
should take the Coord class name and be formatted with snake_case,
so that CoordNew becomes coord_new().
See Also
The new coords section of the online ggplot2 book.
Other Layout components:
Facet,
Layout
Examples
# Extending the class
CoordJitter <- ggproto(
"CoordJitter", CoordCartesian,
# Fields
amount = 0,
# Methods
is_linear = function() FALSE,
transform = function(self, data, panel_params) {
data <- ggproto_parent(CoordCartesian, self)$transform(data, panel_params)
data$x <- jitter(data$x, amount = self$amount)
data$y <- jitter(data$y, amount = self$amount)
data
}
)
# Building a constructor
coord_jitter <- function(amount = 0.005, xlim = NULL, ylim = NULL, expand = TRUE,
clip = "on", reverse = "none") {
ggproto(
NULL, CoordJitter,
amount = amount,
limits = list(x = xlim, y = ylim),
reverse = reverse, expand = expand, clip = clip
)
}
# Use new coord in plot
set.seed(42)
ggplot(mpg, aes(drv, displ)) +
geom_boxplot() +
coord_jitter()
hadley/ggplot2 documentation built on June 13, 2025, 12:51 a.m.
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| Coord | R Documentation |
Coords
Description
All coord_*() functions (like coord_transform()) return a Coord* object
(like CoordTransform). These objects contain methods that support the
coordinate systems in ggplot2.
Details
Each of the Coord* objects is a ggproto() object, descended from the
top-level Coord, and each implements various methods and fields.
The object and its parameters are chaperoned by the Layout class.
To create a new type of Coord object, it is recommended
to extend not the base Coord class, but one of its children like
CoordCartesian.
When overriding the transform() method, it may be necessary to adapt the
implementation of render_bg() and possibly axis placement too.
An important data structure that coordinate systems create is the
panel_params structure. When overriding that structure, many methods may
need to be adapted as well.
Fields
defaultScaler boolean indicating whether this is the default coordinate system. Non-default coordinate systems raise a message when a new system replaces it.
clipA scalar string grid setting controlling whether layers should be clipped to the extent of the plot panel extent. Can be
"on"to perform clipping,"off"to not clip, or"inherit"to take on the setting of the parent viewport.reverseA scalar string giving which directions to reverse. For Cartesian systems, can be
"none,"x","y"or"xy"for both. Non-Cartesian may define their own settings.setup_paramsDescription
A function method for modifying or checking the parameters based on the data. The default method parses the
expandparameter.Usage
Coord$setup_params(data)
Arguments
dataA list of data frames. The first item is the global data, which is followed by layer data in subsequent items.
Value
A list of parameters
setup_dataDescription
A function method for modifying or checking the data prior to adding defaults. The default method returns data unaltered.
Usage
Coord$setup_data(data, params)
Arguments
dataA list of data frames. The first item is the global data, which is followed by layer data in subsequent items.
paramsA list of parameters coming from the
setup_params()method.
Value
A list of data frames of the same length as the
dataargumentsetup_layoutDescription
A function method that acts as a hook for the coordinate system to have input on the layout computed by facets.
Usage
Coord$setup_layout(layout, params)
Arguments
layoutA data frame computed by
Facet$compute_layout(). Typically contains the faceting variables,ROW,COL,PANEL,SCALE_XandSCALE_Yvariables.paramsA list of parameters coming from the
setup_params()method.
Value
A data frame from the modified
layoutargument. The default creates a newCOORDcolumn to identify unique combinations of x and y scales for efficiency purposes. It should never remove columns.modify_scalesDescription
A function method for modifying scales in place. This is optional and currently used by CoordFlip and CoordPolar to ensure axis positions are conforming to the coordinate system.
Usage
Coord$modify_scales(scales_x, scales_y)
Arguments
scales_x,scales_yA list of trained scales for the
xandyaesthetics respectively.
Value
Nothing, this is called for the side effect of modifying scales.
setup_panel_paramsDescription
This function method is used to setup panel parameters per panel. For efficiency reasons, this method is called once per combination of
xandyscales. It is used to instantiate ViewScale class objects and ranges for position aesthetics and optionally append additional parameters needed for thetransform()method and rendering axes.Usage
Coord$setup_panel_params(scale_x, scale_y, params)
Arguments
scale_x,scale_yA list of trained scales for the
xandyaesthetics respectively.paramsA list of parameters coming from the
setup_params()method.
Value
A named list of view scales, ranges and other optional parameters.
setup_panel_guidesDescription
This function method is used to initiate position guides for each panel. For efficiency reasons, this method is called once per combination of
xandyscales. For the primary and secondary positions, it should resolve guides coming from theplot$guidesfield andScale$guidefields and set appropriateGuide$params$positionparameters.Usage
Coord$setup_panel_guides(panel_params, guides, params)
Arguments
panel_paramsA list of ViewScale class objects and additional parameters from the
setup_panel_params()method.guidesA
<Guides>ggproto class.paramsA list of parameters coming from the
setup_params()method.
Value
The
panel_paramsobject but with a Guides class object appended with the name 'guides'.setup_panel_guidesDescription
This function method is used to train and transform position guides for each panel. For efficiency reasons, this method is called once per combination of
xandyscales.Usage
Coord$train_panel_guides(panel_params, layers, params)
Arguments
panel_paramsA list of ViewScale class objects, a Guides class object and additional parameters from the
setup_panel_params()method.layersA list of layers from
plot$layers.paramsA list of parameters coming from the
setup_params()method.
Value
The
panel_paramsobject, but with trained and transformedguidesparameter.transformDescription
This function method is used to apply transformations and rescale position aesthetics. This method is used in several places:
The Geom drawing code, used through
coord_munch()in many Geoms.The Guide transform method
Panel grid transformation in
render_bg()
Usage
Coord$transform(data, panel_params)
Arguments
dataA data frame with columns for numeric position aesthetics.
panel_paramsA list of ViewScale class objects and additional parameters from the
setup_panel_params()method.
Value
The
dataargument with rescaled and transformed position aesthetics.distanceDescription
This function method is used to calculate distances between subsequent data points.
coord_munch()uses this method determine how many points should be used to interpolate.Usage
Coord$distance(x, y, panel_params)
Arguments
x,yx and y coordinates of a set of points in data space.
panel_paramsA list of ViewScale class objects and additional parameters from the
setup_panel_params()method.
Value
The
dataargument with rescaled and transformed position aesthetics.backtransform_rangeDescription
This function method is used to convert ranges from transformed coordinates back into data coordinates. The data coordinates may possibly be scale- transformed. It is used in
coord_munch()to ensure limits are in data coordinates.The back-transformation may be needed for coords such as
coord_transform(), where the range in the transformed coordinates differs from the range in the untransformed coordinates.Usage
Coord$backtransform_range(panel_params)
Arguments
panel_paramsA list of ViewScale class objects and additional parameters from the
setup_panel_params()method.
Value
A list containing numeric ranges for
xandyin data coordinates.rangeDescription
This function method is a small helper method to extract ranges from the
panel_paramsobject. It exists becausepanel_paramscan be opaque at times.Usage
Coord$range(panel_params)
Arguments
panel_paramsA list of ViewScale class objects and additional parameters from the
setup_panel_params()method.
Value
A list containing numeric ranges for
xandy.draw_panelDescription
This function method is used to orchestrate decorating panel drawings with foreground and background drawings. It is called once per panel, invokes the
render_fg()andrender_bg()methods and enforces theclipfield.Usage
Coord$draw_panel(panel, params, theme)
Arguments
panelA grob containing drawn layers and facet foreground and background.
paramsA list of ViewScale class objects and additional parameters from the
setup_panel_params()method.themeA complete theme
Value
A grob with panel content.
render_fgDescription
This function method is used to draw the panel foreground. For all intents and purposes is just the
panel.bordertheme element, but you can repurpose this method.Usage
Coord$render_fg(panel_params, theme)
Arguments
panel_paramsA list of ViewScale class objects and additional parameters from the
setup_panel_params()method.themeA complete theme
Value
A grob with panel foreground.
render_bgDescription
This function method is used to draw the panel background. Typically this is a combination of the
panel.backgroundandpanel.gridtheme elements.Usage
Coord$render_bg(panel_params, theme)
Arguments
panel_paramsA list of ViewScale class objects and additional parameters from the
setup_panel_params()method.themeA complete theme
Value
A grob with panel background.
labelsDescription
This function method is used to format axis titles. It is used in some coordinate systems to (conditionally) swap x and y labels.
Usage
Coord$labels(labels, panel_params)
Arguments
labelsA named list containing an
xlist and aylist. Thexandylists haveprimaryandsecondarylabels.panel_paramsA list of ViewScale class objects and additional parameters from the
setup_panel_params()method.
Value
A list with the same structure and names as the
labelsargument.aspectDescription
This function method that gives the aspect ratio for panels. It allows for
CoordFixedto compute an aspect ratio based on data ranges.Usage
Coord$render_bg(panel_params, theme)
Arguments
rangesA list of ViewScale class objects and additional parameters from the
setup_panel_params()method. If there are multiple panels, the parameters for the first panel is used.
Value
A scalar numeric
render_axis_h,render_axis_vDescription
These function methods are used to render axes to place at the outside edge of panels. Interior axes should not be rendered here. The
render_axis_h()methods produces the horizontal axes for the top and bottom position. Therender_axis_v()method renders the vertical axes for the left and right position.Usage
Coord$render_axis_h(panel_params, theme Coord$render_axis_v(panel_params, theme)
Arguments
panel_paramsA list of ViewScale class objects, a Guides class object and additional parameters from the
setup_panel_params()method.themeA complete theme
Value
For
render_axis_h()a named list where"top"and"bottom"are grobs with an axis. Forrender_axis_v()a named list where"left"and"right"are grobs with an axis. These grobs should bezeroGrob()when no axes should be rendered.is_linearDescription
This function method is used to signal whether a coordinate system is linear. In
coord_munch()and several Geom drawing methods, it is used to determine whether points should be interpolated.Usage
Coord$is_linear()
Value
A scalar boolean.
is_freeDescription
This function method is used to signal whether a coordinate system supports free scaling of axes in faceted plots. This should generally return
FALSEfor coordinate systems that enforce a fixed aspect ratio.Usage
Coord$is_free()
Value
A scalar boolean.
Conventions
The object name that a new class is assigned to is typically the same as the
class name. Coord class names are in UpperCamelCase and start with the
Coord* prefix, like CoordNew.
A constructor function is usually paired with a Coord class. The constructor
copies the coord class and populates parameters. The constructor function name
should take the Coord class name and be formatted with snake_case,
so that CoordNew becomes coord_new().
See Also
The new coords section of the online ggplot2 book.
Other Layout components:
Facet,
Layout
Examples
# Extending the class
CoordJitter <- ggproto(
"CoordJitter", CoordCartesian,
# Fields
amount = 0,
# Methods
is_linear = function() FALSE,
transform = function(self, data, panel_params) {
data <- ggproto_parent(CoordCartesian, self)$transform(data, panel_params)
data$x <- jitter(data$x, amount = self$amount)
data$y <- jitter(data$y, amount = self$amount)
data
}
)
# Building a constructor
coord_jitter <- function(amount = 0.005, xlim = NULL, ylim = NULL, expand = TRUE,
clip = "on", reverse = "none") {
ggproto(
NULL, CoordJitter,
amount = amount,
limits = list(x = xlim, y = ylim),
reverse = reverse, expand = expand, clip = clip
)
}
# Use new coord in plot
set.seed(42)
ggplot(mpg, aes(drv, displ)) +
geom_boxplot() +
coord_jitter()
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