How to remove function from list in R?

Question

I have list with two functions:

foo <- function() { print('foo') }
bar <- function() {}
l <- list(foo, bar)

How can I remove function foo without knowing its index?

I've tried this (to get indexes for sub setting):

> which(l == foo)
Error in l == foo : 
  comparison (1) is possible only for atomic and list types

Is there easy way to remove non-atomic from list without looping?

Answer 1

Assuming the code in the question, use identical we can get its index like this:

Position(function(fun) identical(fun, foo), l)
## [1] 1

or

which(sapply(l, identical, foo))
## [1] 1

If you know something about the functions you may be able to run them and select based on the output. For the example this works:

Position(function(f) length(f()), l)
## [1] 1

If you have control over the creation of the list an easy approach is to create the list with names:

l2 <- list(foo = foo, bar = bar)
nms <- setdiff(names(l2), "foo")

Removal

If we know that foo is in l once then

l[-ix]

or in the case of l2:

l2[nms]

or use the alternative given by @Gregor:

Filter(function(x) !identical(x, foo), l)

Edge cases

If foo might not be in l you will need to check that condition first. Position and match return NA if there is no match (or specify the nomatch argument to either) and which returns intetger(0) for a no match.

If foo can be in l more than once then use the which alternative above.

Other

Note that which and Filter check every position but match and Position stop after the first match.