In R, how do I test that two functions have the same definition?

Question

I have two functions, f and g, which have the same definition:

f <- function(x) { x + 1 }
g <- function(x) { x + 1 }

However, the identical function considers them different:

identical(f, g)
FALSE

I presume this is because they occupy different areas in memory; identical(f, f) gives TRUE.

I am only interested in testing that the functions having the same definition; is there another function I can use for this?

The behaviour should be:

sameDefinition(f, f)
TRUE

sameDefinition(f, g)
TRUE

sameDefinition(f, function(x) { x + 1 })
TRUE

sameDefinition(f, function(x) { x + 3 }) 
FALSE 

# Equivalent, but different definitions
sameDefinition(f, function(x) { x + 2 - 1 }) 
FALSE

You can try `all.equal` (found while reading `?identical` in the see-also part) — Tensibai, Aug 28 '15 at 08:31
A function consists of more than just a body. Even the body has things in addition to the text. If you want to compare only the text in the body try `identical(as.character(body(g)), as.character(body(f)))` — user20637, Aug 28 '15 at 12:22

score 8 · Accepted Answer · answered Aug 28 '15 at 08:40

Long version of my comment:

Quote of ?identical doc:

See Also

all.equal for descriptions of how two objects differ;

In the all.equal doc there's:

Do not use all.equal directly in if expressions—either use isTRUE(all.equal(....)) or identical if appropriate.

So you don't really need a function, you can write isTRUE(all.equal(f,g)) and be done with your task.

score 4 · Answer 2 · answered Aug 28 '15 at 09:58

4

You could deparse the functions and then check if they are identical:

identical(deparse(f),deparse(g))
[1] TRUE

answered Aug 28 '15 at 09:58

James

65,548
14
155
193

sdgfsdh · Answer 3 · 2015-08-28T15:21:19.980

1

As suggested by Tensibai, you can use the all.equal function. A wrapper is required since all.equal will return a character vector when the objects are not equal.

sameDefinition <- function(x, y) { 

    stopifnot(is.function(x), "x must be a function")
    stopifnot(is.function(y), "y must be a function")

    identical(all.equal(x, y), TRUE)
}

Examples:

sameDefinition(f, g)
TRUE

sameDefinition(f, function(x) { x + 2 - 1 })
FALSE

edited Aug 28 '15 at 15:21

answered Aug 28 '15 at 08:37

sdgfsdh

33,689
26
132
245

Why not using directly isTRUE as per all.equal documentation ? – Tensibai Aug 28 '15 at 08:38
`isTRUE` is just `identical(TRUE, x)` - I suppose either approach is valid. – sdgfsdh Aug 28 '15 at 08:39
2

`identical(TRUE, x)` is not the same as `x == TRUE`. Try them with `x <- "TRUE"`. And you should use `TRUE` instead of `T`, since `T` can be redefined and `TRUE` cannot. – Joshua Ulrich Aug 28 '15 at 14:43
I wasn't aware of that - updated the answer accordingly. – sdgfsdh Aug 28 '15 at 15:21

In R, how do I test that two functions have the same definition?

3 Answers3