Modify permutations function to take a size argument

[kmsquire]

As seen here:

In Python, you can use itertools to generate permutations like so:

>>> list(itertools.permutations("ABC", 2))
 [('A', 'B'), ('A', 'C'), ('B', 'A'), ('B', 'C'), ('C', 'A'), ('C', 'B')]
 Julia has a similar permutations function, but it only accepts one argument.

It woulds be a reasonable extension of the permutations function to add this.

[IainNZ]

Why is it reasonable?

[kmsquire]

This functionality is something that at least I have used in the past (in Python), and it should be a fairly straightforward extension to the existing functionality.

Why wouldn't it be reasonable? I'm open to counter arguments.

[kmsquire]

I do also think that the permutations function should probably be moved out of Base (assuming it isn't used, of course).

[IainNZ]

It just seems like one more thing to add for the sake of it, when it should really be in a package (or you can do what I proposed on SO).

[IainNZ]

I don't have strong feelings either way to be honest, but I do lean towards not adding it to Base. Certainly think it should be questioned.

[kmsquire]

(or you can do what I proposed on SO)

Sure.

julia> collect(chain([permutations(x) for x in subsets(collect("ABC"), 2)]...))
6-element Array{Array{Char,1},1}:
 ['A','B']
 ['B','A']
 ['A','C']
 ['C','A']
 ['B','C']
 ['C','B']

I think that would take a little while for most users to figure out if they aren't familiar with the Iterators.jl package. And I find it rather ugly.

(But I really would have no problem if the functionality suggested here were added there instead.)

[kmsquire]

(But if it's put in Iterators.jl, I think it would make sense to move the current permutations function at the same time.)

[mschauer]

Please, permutations certainly belong to base. As a data point: permute is one of the selected primitives in J, http://www.jsoftware.com/help/dictionary/vocabul.htm

[AnishShah]

Hi. If anybody else is not working on this, then can I work on this?

[malmaud]

@AnishShah You sure can - it would be appreciated.

[catchmrbharath]

@AnishShah Are you still working on this?

[rawls238]

can probably close this since this has been moved out of Base?

[tkelman]

Yep, good call, closed by #13897. Could be reopened as a feature request at Combinatorics.jl though.