How to determine if one array contains all elements of another array

Question

Given   a1    5  1  6  14  2  8    I would like to determine if it contains all elements of   a2    2  6  15    In this case the result is false   Are there any built-in Ruby Rails methods to identify such array inclusion   One way to implement this is   a2 index   x   a1 include  x    nil    Is there a better  more readable  way

User · Answer

If there are are no duplicate elements or you don't care about them, then you can use the Set class:

a1 = Set.new [5, 1, 6, 14, 2, 8]
a2 = Set.new [2, 6, 15]
a1.subset?(a2)
=> false

Behind the scenes this uses

all? { |o| set.include?(o) }

User · Answer

Perhaps this is easier to read   a2 all     e  a1 include  e      You can also use array intersection    a1  amp  a2  size    a1 size   Note that size is used here just for speed  you can also do  slower     a1  amp  a2     a1   But I guess the first is more readable  These 3 are plain ruby  not rails

User · Answer

You can monkey-patch the Array class   class Array     def contains all  ary          ary uniq all     x  count x   gt   ary count x        end end   test  irb main  131 0 gt   w a b c c  contains all   w a b c    gt  true irb main  132 0 gt   w a b c c  contains all   w a b c c    gt  true irb main  133 0 gt   w a b c c  contains all   w a b c c c    gt  false irb main  134 0 gt   w a b c c  contains all   w a    gt  true irb main  135 0 gt   w a b c c  contains all   w x    gt  false irb main  136 0 gt   w a b c c  contains all   w     gt  true irb main  137 0 gt   w a b c d  contains all   w d c h    gt  false irb main  138 0 gt   w a b c d  contains all   w d b c    gt  true   Of course the method can be written as a standard-alone method  eg  def contains all  a b      b uniq all     x  a count x   gt   b count x    end   and you can invoke it like  contains all   w a b c c    w c c c     Indeed  after profiling  the following version is much faster  and the code is shorter   def contains all  a b      b all     x  a count x   gt   b count x    end

User · Answer

This can be achieved by doing   a2  amp  a1     a2   This creates the intersection of both arrays  returning all elements from a2 which are also in a1  If the result is the same as a2  you can be sure you have all elements included in a1   This approach only works if all elements in a2 are different from each other in the first place  If there are doubles  this approach fails  The one from Tempos still works then  so I wholeheartedly recommend his approach  also it s probably faster

User · Answer

a    5  1  6  14  2  8  b    2  6  15   a - b     gt   5  1  14  8   b - a     gt   15    b - a  empty      gt  false

User · Answer

Depending on how big your arrays are you might consider an efficient algorithm O n log n   def equal a a1  a2    a1sorted   a1 sort   a2sorted   a2 sort   return false if a1 length    a2 length   0 upto a1 length - 1  do       i  return false if a1sorted i     a2sorted i    end end   Sorting costs O n log n  and checking each pair costs O n  thus this algorithm is O n log n   The other algorithms cannot be faster  asymptotically  using unsorted arrays

User · Answer

Most answers based on  a1 - a2  or  a1  amp  a2  would not work if there are duplicate elements in either array  I arrived here looking for a way to see if all letters of a word  split to an array  were part of a set of letters  for scrabble for example   None of these answers worked  but this one does   def contains all  a1  a2    try   a1 chars all  do  letter      a1 count letter   lt   a2 count letter    end   return try end

[ruby-on-rails] How to determine if one array contains all elements of another array

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