Feature #16155
closedAdd an Array#intersection method
Description
Array#union
and Array#difference
were added in Ruby 2.6 (see this bug), but an equivalent for &
(intersection) was not.
I'd like to propose Array#intersection
. This would essentially just be a more readable alias for Array#&
, in the same way that Array#|
and Array#-
have Array#union
and Array#difference
.
I think it'd make sense for Ruby to have a more readable name for this method :)
Current syntax:
[ 1, 1, 3, 5 ] & [ 3, 2, 1 ] #=> [ 1, 3 ]
[ 'a', 'b', 'b', 'z' ] & [ 'a', 'b', 'c' ] #=> [ 'a', 'b' ]
What I'd like to see added:
[ 1, 1, 3, 5 ].intersection([ 3, 2, 1 ]) #=> [ 1, 3 ]
[ 'a', 'b', 'b', 'z' ].intersection([ 'a', 'b', 'c' ]) #=> [ 'a', 'b' ]
mame asks about intersection
in this comment on the union
/difference
bug, but as far as I can tell it was never addressed.
Set#intersection
already exists and is an alias for Set#&
, so there's precedent for such a method to exist.
Thanks for Ruby, I enjoy using it a lot! :)
Related links:
Updated by shevegen (Robert A. Heiler) about 5 years ago
I sort of agree with your reasoning. A slight add-on, though,
on that part:
This would essentially just be a more readable alias for Array#&
It is probably easier to search for it (e. g. a google-search for
.intersection) than for &. But if we compare relative merits then
we also have to remember an advantage for & being that it is
short/succinct.
It's an aside, though, because I agree with your reasoning anyway;
it would make sense to also have .intersection, IMO. :)
You could consider adding this to the upcoming developer meeting:
https://bugs.ruby-lang.org/issues/16152
And ask matz whether he would be fine with the functionality
itself; or, more importantly, the name for the method
(#intersection) since the functionality already exists.
Updated by connorshea (Connor Shea) about 5 years ago
shevegen (Robert A. Heiler) wrote:
You could consider adding this to the upcoming developer meeting:
https://bugs.ruby-lang.org/issues/16152
And ask matz whether he would be fine with the functionality
itself; or, more importantly, the name for the method
(#intersection) since the functionality already exists.
Thanks, I will :)
After thinking about the proposal a bit more, one other thing I wanted to ask was about whether we should allow multiple arrays to be passed as arguments. Array#difference
and Array#union
both allow this, so it might make sense to have Array#intersection
also take multiple arguments.
For example:
# intersection with multiple arguments.
[ 'a', 'b', 'b', 'z' ].intersection([ 'a', 'b', 'c' ], [ 'b' ]) #=> [ 'b' ]
Should we keep intersection
as a simple alias for &
or have it allow multiple arrays, to match the difference
and union
methods?
Updated by phluid61 (Matthew Kerwin) about 5 years ago
connorshea (Connor Shea) wrote:
Should we keep
intersection
as a simple alias for&
or have it allow multiple arrays, to match thedifference
andunion
methods?
The question should be: is it needed?
Updated by matz (Yukihiro Matsumoto) about 5 years ago
Accepted. PR welcome.
Matz.
Updated by prajjwal (Prajjwal Singh) about 5 years ago
Hi all,
I've added an initial implementation of this based on Array#&
on github (https://github.com/ruby/ruby/pull/2533).
One thing that stands out to me is the naming inconsistency between rb_ary_and
and rb_ary_intersection_multi
, and I think either could be changed to be consistent with the other. Thoughts?
Updated by prajjwal (Prajjwal Singh) about 5 years ago
Implementation is currently based on Array#&
, which is elegant but might end up allocating a whole bunch of arrays holding intermediate results. If needed I can implement Array#intersection
so it only allocates the result array once, but then I would like to rewrite Array#&
in terms of Array#intersection
to keep things DRY.
static VALUE
rb_ary_intersection_multi(int argc, VALUE *argv, VALUE ary)
{
VALUE result = rb_ary_dup(ary);
int i;
for (i = 0; i < argc; i++) {
result = rb_ary_and(result, argv[i]);
}
return result;
}
Let me know what you think.
Updated by nobu (Nobuyoshi Nakada) about 5 years ago
- Status changed from Open to Closed