Whats the algorithm that Array#include? uses?

Question

For ruby where x is an array, how does x.include?(y) check if y is in x? What's the algorithm?

you can find the source of the function ruby-doc.org/core-1.9.3/Array.html#method-i-include-3F — Benoît
– Benoît, Commented Jan 27, 2012 at 1:22

blahman · Accepted Answer · 2012-01-27 01:24:03Z

6

As an addition to Greg Hewgill's answer, the source code from Ruby 1.9.3 for this method is:

VALUE
rb_ary_includes(VALUE ary, VALUE item)
{
    long i;

    for (i=0; i<RARRAY_LEN(ary); i++) {
        if (rb_equal(RARRAY_PTR(ary)[i], item)) {
            return Qtrue;
        }
    }
    return Qfalse;
}

Thus, as Greg has said, the algorithm is just a linear search through the array.

answered Jan 27, 2012 at 1:24

blahman

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Greg Hewgill · Accepted Answer · 2012-01-27 01:19:52Z

3

Since the array does not have to be sorted, the algorithm cannot be anything better than "look at each element and see if it matches".

answered Jan 27, 2012 at 1:19

Greg Hewgill

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4 Comments

Mark Thomas Over a year ago

@cfarm54 With a large sorted array a binary search would be faster in most cases. 0xcc.net/ruby-bsearch/index.html.en

locoboy Over a year ago

yep, and i assume there are no functions for this in ruby

Mark Thomas Over a year ago

@cfarm54 There are several. In fact I linked to one in my previous comment.

Mark Thomas Over a year ago

As @Marc-AndréLafortune mentioned, the Ruby builtin Set is even better, as its members are stored as a Hash internally.

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