From: "Eric I." <rubytraining@...>
Date: 2007-10-10T07:05:08+09:00
Subject: Re: Finding shared elements between to arrays.

On Oct 9, 5:46 pm, Sebastian probst Eide
<sebastian.probst.e...@gmail.com> wrote:
> Hi
> I am wondering if there is a really smart built in way to get an array
> which has the elements shared by two other arrays? I made two
> "solutions" myself, but I am wondering what other people are using, and
> if there is a preferred solution to the task? array.union(other_array)
> or something like that?

The & operator, as defined on Arrays, performs an intersection
operation.

>From the RDoc:

> array & other_array
> ------------------------------------------------------------------------
>      Set Intersection---Returns a new array containing elements common
>      to the two arrays, with no duplicates.
>
>         [ 1, 1, 3, 5 ] & [ 1, 2, 3 ]   #=> [ 1, 3 ]

Also, another tip: rather than using a combination of map and
compact!, you could instead use select, as in:

    a3 = a1.select { |e| a2.include?(e) }

Best,

Eric

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