R: all.equal() for multiple objects?

Question

What is the best way to compare more than two objects with all.equal()?

Here's one way:

foo <- c(1:10)
bar <- letters[1:10]
baz <- c(1:10)

# doesn't work because all.equal() returns a character vector when objects not all equal
  all(sapply(list(bar, baz), all.equal, foo))

# this works
  mode(sapply(list(bar, baz), all.equal, foo)) == "logical" #FALSE

  bar <- c(1:10)

  mode(sapply(list(bar, baz), all.equal, foo)) == "logical" #TRUE

UPDATE: @BrodieG pointed out that the one-liner above only tells you whether the objects are all equal or not, whereas all.equal() tells you what isn't equal about them if they aren't equal.

Answer 1

Here is an option:

objs <- mget(c("foo", "bar", "faz"))
outer(objs, objs, Vectorize(all.equal))

It's better than yours because it will detect when bar and faz are the same, even when foo isn't. That said, it does a lot of unnecessary comparisons and will be slow. For example, if we change foo to be letters[1:10] we get:

    foo         bar         faz        
foo TRUE        Character,2 Character,2
bar Character,2 TRUE        TRUE       
faz Character,2 TRUE        TRUE 

For details on what went wrong, just subset:

outer(objs, objs, Vectorize(all.equal))[1, 2]

Produces:

[[1]]
[1] "Modes: character, numeric"              
[2] "target is character, current is numeric"       

If all you care about is that all the objects must be all.equal, then your solution is pretty good.

Also, as per comments to limit some of the duplicate calculations:

res <- outer(objs, objs, function(x, y) vector("list", length(x)))
combs <- combn(seq(objs), 2)
res[t(combs)] <- Vectorize(all.equal)(objs[combs[1,]], objs[combs[2,]])
res

Produces

    foo  bar         faz        
foo NULL Character,2 Character,2
bar NULL NULL        TRUE       
faz NULL NULL        NULL         

This still shows the full matrix, but makes it obvious what comparisons produced what.