arrayOps: Operations on CFVariable objects

In ncdfCF: Easy Access to NetCDF Files with CF Metadata Conventions

Operations on CFVariable objects

Description

Basic arithmetic, mathematical and logical operations can be applied on the data of CFVariable objects having a suitable data type, specifically the base R functions from the Ops and Math groups of the S3 groupGeneric functions.

Usage

## S3 method for class 'CFVariable'
Ops(e1, e2)

## S3 method for class 'CFVariable'
Math(x, ...)

Arguments

e1, e2	CFVariable objects, or a single numeric value.
x	A CFVariable object.
...	Additional arguments passed on to the math functions.

Details

The functions always return a new CFVariable object. Functions can thus be concatenated to create more complex expressions. The data type of the new object is determined by the base R function; its name is concatenated from the names in the argument object(s).

For the Ops functions with two arguments, if both arguments are a CFVariable object they have to be compatible: same shape, axis coordinate values and coordinate reference system. The resulting CFVariable object will use the same axes as the CFVariable object(s) used as argument.

The attributes of the resulting CFVariable object should be updated to reflect its contents, in particular the "name", "long_name", "standard_name" and "units" attributes. Attributes are not copied over from the CFVariable objects in the arguments.

Value

A new CFVariable object. The object will have the same coordinate space as the CFVariable object used as argument. Arguments are not copied and the new object will only have the "actual_range" attribute set.

Results that are logical (see the examples) are stored using the NC_SHORT data type because netCDF does not have a native logical data type.

Examples

fn <- system.file("extdata", "ERA5land_Rwanda_20160101.nc", package = "ncdfCF")
ds <- open_ncdf(fn)

# Temperature data in K
t2m <- ds[["t2m"]]

# Convert to degrees_Celsius
t2mC <- t2m - 273.15
t2mC$name <- "t2m_Celsius"
t2mC$set_attribute("units", "NC_CHAR", "degrees_Celsius")
t2mC

hot <- t2mC > 20
hot$name <- "t2m_Celsius_over_20"
hot$set_attribute("long_name", "NC_CHAR", "Flag to indicate where temperature is 20C or hotter")
hot$set_attribute("units", "NC_CHAR", "1")
hot

ncdfCF documentation built on Sept. 13, 2025, 5:07 p.m.