What is the %||% operator?

sam81 · July 19, 2018, 10:54am

I'm trying to create a custom ggplot2 geom by modifying geom_errorbar. The geom_errorbar function uses an operator that I've never seen before %||%, on line 37 here:

github.com

tidyverse/ggplot2/blob/master/R/geom-errorbar.r

#' @export
#' @rdname geom_linerange
geom_errorbar <- function(mapping = NULL, data = NULL,
                          stat = "identity", position = "identity",
                          ...,
                          na.rm = FALSE,
                          show.legend = NA,
                          inherit.aes = TRUE) {
  layer(
    data = data,
    mapping = mapping,
    stat = stat,
    geom = GeomErrorbar,
    position = position,
    show.legend = show.legend,
    inherit.aes = inherit.aes,
    params = list(
      na.rm = na.rm,
      ...
    )

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does anyone know what it is, and which package define it? Trying to run my custom geom I get the error:

Error in data$width %||% params$width %||% (resolution(data$x, FALSE) *  (from geom_errorbar2.R#40) : 
  could not find function "%||%"

mara · July 19, 2018, 11:14am

%||% is an operator from rlang to that lets you replace the default value for NULL.

From rlang docs:

This infix function makes it easy to replace NULLs with a default value. It's inspired by the way that Ruby's or operation (||) works.

It takes arguments x and y, where if x is NULL, will return y; otherwise returns x.

x %||% y

The reason your code doesn't work (I assume, from your snippet above) is because you need to import the function %||% in order to use it.

You can see the Specifying imports and exports section of Writing R Extensions, or the Namespace section of the R Packages book for more detail.

sam81 · July 19, 2018, 11:27am

thank you very much for the very informative answer! I'm able to run my custom geom by loading the rlang package.