R Tip: use isTRUE()

[This article was first published on R – Win-Vector Blog, and kindly contributed to R-bloggers]. (You can report issue about the content on this page here)
Want to share your content on R-bloggers? click here if you have a blog, or here if you don't.

R Tip: use isTRUE().

A lot of R functions are type unstable, which means they return different types or classes depending on details of their values.

For example consider all.equal(), it returns the logical value TRUE when the items being compared are equal:

all.equal(1:3, c(1, 2, 3))
# [1] TRUE

However, when the items being compared are not equal all.equal() instead returns a message:

all.equal(1:3, c(1, 2.5, 3))
# [1] "Mean relative difference: 0.25"

This can be inconvenient in using functions similar to all.equal() as tests in if()-statements and other program control structures.

The saving functions is isTRUE(). isTRUE() returns TRUE if its argument value is equivalent to TRUE, and returns FALSE otherwise. isTRUE() makes R programming much easier.

Some examples of isTRUE() are given below:

isTRUE(TRUE)
# [1] TRUE

isTRUE(FALSE)
[1] FALSE

isTRUE(NULL)
# [1] FALSE

isTRUE(NA)
# [1] FALSE

isTRUE(all.equal(1:3, c(1, 2.5, 3)))
# [1] FALSE

isTRUE(all.equal(1:3, c(1, 2, 3)))
# [1] TRUE

lst <- list(x = 5)
isTRUE(lst$y == 7)
# [1] FALSE
lst$y == 7

logical(0)
isTRUE(logical(0))
# [1] FALSE

Using isTRUE() one can write safe and legible code such as the following:

# Pretend this assignment was performed by somebody else.
lst <- list(x = 5)

# Our own sanitization code.
if(!isTRUE(lst$y > 3)) {
  lst$y = lst$x
}

print(lst)

# $x
# [1] 5
#
# $y
# [1] 5

R now also has isFALSE(), but by design it does not mean the same thing as !isTRUE(). The ideas is: for a value v at most of one of isTRUE() or isFALSE() is set, and both are non-NA unnamed scalar logical values. (example: isTRUE(5), isFALSE(5)).

Or as help(isTRUE) puts it:

… if(isTRUE(cond)) may be preferable to if(cond) …

Note: prior to R 3.5 isTRUE (the current version!) was defined as “isTRUE <- function(x) identical(x, TRUE)” (please see change-log here). This seemed clever, but failed on named logical values (violating a principle of least surprise):

oldTRUE <- function(x) identical(x, TRUE)

v <- TRUE
oldTRUE(v)
# [1] TRUE
isTRUE(v)
# [1] TRUE

names(v) <- "condition"
oldTRUE(v)
# [1] FALSE
isTRUE(v)
# [1] TRUE

This caused a lot of problems (example taken from R3.5.0 NEWS):

x <- rlnorm(99)

isTRUE(median(x) == quantile(x)["50%"])
# [1] TRUE

oldTRUE(median(x) == quantile(x)["50%"])
# [1] FALSE

To leave a comment for the author, please follow the link and comment on their blog: R – Win-Vector Blog.

R-bloggers.com offers daily e-mail updates about R news and tutorials about learning R and many other topics. Click here if you're looking to post or find an R/data-science job.
Want to share your content on R-bloggers? click here if you have a blog, or here if you don't.

Never miss an update!
Subscribe to R-bloggers to receive
e-mails with the latest R posts.
(You will not see this message again.)

Click here to close (This popup will not appear again)