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

Question

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  lt  lt  Horse find  first  offset  gt rand Horse count     while  suggested horses length  lt  8     horse   Horse find  first  offset  gt rand Horse count       unless  suggested horses exists  horse id          suggested horses lt  lt  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   lt Array 0xc11c0b8 gt    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

User · Accepted Answer

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  lt  lt  horse end   should work out of box

User · Answer

Array s include method accepts any object  not just a string  This should work    suggested horses        suggested horses  lt  lt  Horse first  offset   gt  rand Horse count    while  suggested horses length  lt  8    horse   Horse first  offset   gt  rand Horse count       suggested horses  lt  lt  horse unless  suggested horses include  horse  end    Array include  documentation

User · Answer

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  lt  lt  horse end

User · Answer

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 lt  lt  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  lt  lt  horse end   ActiveRecord has redefined comparision operator for objects to take a look only for its state  new created  and id

User · Answer

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   gt  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

User · Answer

This      horse   Horse find  first  offset  gt rand Horse count   unless  suggested horses exists  horse id      suggested horses lt  lt  horse end   Should probably be this      horse   Horse find  first  offset  gt rand Horse count   unless  suggested horses include  horse      suggested horses lt  lt  horse end

User · Answer

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     gt    a   gt nil   b   gt nil  hash  a     nil hash     gt    a   gt nil   b   gt nil   require  set  ary      to set ary  lt  lt   a  ary  lt  lt   b  ary     gt    lt Set    a    b   gt  ary  lt  lt   a  ary     gt    lt Set    a    b   gt    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  lt  lt  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

[ruby-on-rails] How do I check to see if my array includes an object?

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