How to check if a function is in a vector in R?

Question

I want to do do something like pnorm %in% c(pnorm, pt, pchisq) , but this doesn't work.

What could I do instead?

Answer 1

A solution with purrr:

has_element(c(pt,pnorm,pchisq),pnorm)
#[1] TRUE
has_element(c(pt,pchisq),pnorm)
#[1] FALSE

Answer 2

pnorm %in% c(pnorm, pt, pchisq)

results in error :

Error in match(x, table, nomatch = 0L) : 'match' requires vector arguments

Indeed %in% calls match and ?match tells us (slightly reformatted):

x : vector or NULL: the values to be matched.

We can make it work by making your function a 1 element list :

list(pnorm) %in% c(pnorm, pt, pchisq)
# [1] TRUE

However, a more idiomatic way of doing what you want is to apply the function identical on your list of functions, it will loop on your function elements and check for each one if it's identical to pnorm :

sapply(c(pnorm, pt, pchisq), identical, pnorm)
# [1]  TRUE FALSE FALSE

To get a your desired output, wrap inside any :

any(sapply(c(pnorm, pt, pchisq), identical, pnorm))
# [1] TRUE

These 2 methods are not strictly equivalent however because identical is more strict and will check the environment while the first solution will only check the arguments and body (ie the output of as.list(fun)), see :

pnorm2 <- function (q, mean = 0, sd = 1, lower.tail = TRUE, log.p = FALSE) 
  .Call(C_pnorm, q, mean, sd, lower.tail, log.p)

environment(pnorm2)
# <environment: R_GlobalEnv>
environment(pnorm)
# <environment: namespace:stats>

any(sapply(c(pnorm, pt, pchisq), identical, pnorm2))
# [1] FALSE
list(pnorm2) %in% c(pnorm, pt, pchisq)
# [1] TRUE

Answer 3

`%inl%` <- function(z,l) !is.null(Find(function(x) identical(x,z),l))
pnorm %inl% c(pt,pchisq)
#[1] FALSE
pnorm %inl% c(pt,pnorm,pchisq)
#[1] TRUE