CODEWITHSUNDEEP
ruby-on-railsruby
necker
necker

Reputation: 7173

How do I check to see if my array includes an object?

I have an array @horses = [] that I fill with some random horses.

How can I check if my @horses array includes a horse that is already included (exists) in it?

I tried something like:

@suggested_horses = []
  @suggested_horses << Horse.find(:first,:offset=>rand(Horse.count))
  while @suggested_horses.length < 8
    horse = Horse.find(:first,:offset=>rand(Horse.count))
    unless @suggested_horses.exists?(horse.id)
       @suggested_horses<< horse
    end
  end

I also tried with include? but I saw it was for strings only. With exists? I get the following error:

undefined method `exists?' for #<Array:0xc11c0b8>

So the question is how can I check if my array already has a "horse" included so that I don't fill it with the same horse?

Upvotes: 86

Views: 176659

Answers (7)

David Hempy
David Hempy

Reputation: 6287

An alternative to horses.include? new_horse is new_horse.in? horses.

I don't think there's much (any?) difference under the hood, but sometimes it reads better that way. Particularly if you want the first term to explain a bit more of what is going on before reading the entire statement. For example, this:

[403, 404, 503].include? http_status

...is not as readable as:

http_status.in? [403, 404, 503]

Upvotes: 1

Tomasz Cudziło
Tomasz Cudziło

Reputation: 2492

Arrays in Ruby don't have exists? method, but they have an include? method as described in the docs. Something like

unless @suggested_horses.include?(horse)
   @suggested_horses << horse
end

should work out of box.

Upvotes: 188

Andrew
Andrew

Reputation: 239167

If you want to check if an object is within in array by checking an attribute on the object, you can use any? and pass a block that evaluates to true or false:

unless @suggested_horses.any? {|h| h.id == horse.id }
  @suggested_horses << horse
end

Upvotes: 33

the Tin Man
the Tin Man

Reputation: 160631

So the question is how can I check if my array already has a "horse" included so that I don't fill it with the same horse?

While the answers are concerned with looking through the array to see if a particular string or object exists, that's really going about it wrong, because, as the array gets larger, the search will take longer.

Instead, use either a Hash, or a Set. Both only allow a single instance of a particular element. Set will behave closer to an Array but only allows a single instance. This is a more preemptive approach which avoids duplication because of the nature of the container.

hash = {}
hash['a'] = nil
hash['b'] = nil
hash # => {"a"=>nil, "b"=>nil}
hash['a'] = nil
hash # => {"a"=>nil, "b"=>nil}

require 'set'
ary = [].to_set
ary << 'a'
ary << 'b'
ary # => #<Set: {"a", "b"}>
ary << 'a'
ary # => #<Set: {"a", "b"}>

Hash uses name/value pairs, which means the values won't be of any real use, but there seems to be a little bit of extra speed using a Hash, based on some tests.

require 'benchmark'
require 'set'

ALPHABET = ('a' .. 'z').to_a
N = 100_000
Benchmark.bm(5) do |x|
  x.report('Hash') { 
    N.times {
      h = {}
      ALPHABET.each { |i|
        h[i] = nil
      }
    }
  }

  x.report('Array') {
    N.times {
      a = Set.new
      ALPHABET.each { |i|
        a << i
      }
    }
  }
end

Which outputs:

            user     system      total        real
Hash    8.140000   0.130000   8.270000 (  8.279462)
Array  10.680000   0.120000  10.800000 ( 10.813385)

Upvotes: 2

Marc-Andr&#233; Lafortune
Marc-Andr&#233; Lafortune

Reputation: 79622

Why not do it simply by picking eight different numbers from 0 to Horse.count and use that to get your horses?

offsets = (0...Horse.count).to_a.sample(8)
@suggested_horses = offsets.map{|i| Horse.first(:offset => i) }

This has the added advantage that it won't cause an infinite loop if you happen to have less than 8 horses in your database.

Note: Array#sample is new to 1.9 (and coming in 1.8.8), so either upgrade your Ruby, require 'backports' or use something like shuffle.first(n).

Upvotes: 3

MBO
MBO

Reputation: 31025

#include? should work, it works for general objects, not only strings. Your problem in example code is this test:

unless @suggested_horses.exists?(horse.id)
  @suggested_horses<< horse
end

(even assuming using #include?). You try to search for specific object, not for id. So it should be like this:

unless @suggested_horses.include?(horse)
  @suggested_horses << horse
end

ActiveRecord has redefined comparision operator for objects to take a look only for its state (new/created) and id

Upvotes: 3

John Topley
John Topley

Reputation: 115422

Array's include?method accepts any object, not just a string. This should work:

@suggested_horses = [] 
@suggested_horses << Horse.first(:offset => rand(Horse.count)) 
while @suggested_horses.length < 8 
  horse = Horse.first(:offset => rand(Horse.count)) 
  @suggested_horses << horse unless @suggested_horses.include?(horse)
end

Upvotes: 1

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