Removing elements from array Ruby

Question

Let s say I am trying to remove elements from array a    1 1 1 2 2 3   If I perform the following   b   a -  1 3    Then I will get   b    2 2    However  I want the result to be  b    1 1 2 2    i e  I only remove one instance of each element in the subtracted vector not all cases  Is there a simple way in Ruby to do this

User · Answer

A simple solution I frequently use   arr     remove me  3 4 2 45   arr 1  -1     gt   3 4 2 45

User · Answer

a    1 1 1 2 2 3  a slice  0    remove first index a slice  -1    remove last index   a    1 1 2 2  as desired

User · Answer

1 3  inject  1 1 1 2 2 3   do  memo element    memo tap do  memo      i   memo find index e      memo delete at i  if i   end end

User · Answer

For speed  I would do the following  which requires only one pass through each of the two arrays  This method preserves order  I will first present code that does not mutate the original array  then show how it can be easily modified to mutate   arr    1 1 1 2 2 3 1  removals    1 3 1   h   removals group by  amp  itself  transform values  amp  size       gt   1  gt 2  3  gt 1   arr each with object        n a    h key  n   amp  amp  h n   gt  0    h n  -  1    a  lt  lt  n        gt   1  2  2  1   arr      gt   1  1  1  2  2  3  1     To mutate arr write   h   removals group by  amp  itself  transform values  amp  count  arr replace arr each with object        n a    h key  n   amp  amp  h n   gt  0    h n  -  1    a  lt  lt  n         gt   1  2  2  1   arr      gt   1  2  2  1    This uses the 21st century method Hash transform values  new in MRI v2 4   but one could instead write   h   Hash removals group by  amp  itself  map    k v   k v size       or  h   removals each with object Hash new 0       n h  h n     1

User · Answer

Not very simple but   a    1 1 1 2 2 3  b   a group by   n  n  each   k v  v pop  1 3  count k   values flatten   gt   1  1  2  2    Also handles the case for multiples in the  subtrahend    a    1 1 1 2 2 3  b   a group by   n  n  each   k v  v pop  1 1 3  count k   values flatten   gt   1  2  2    EDIT  this is more an enhancement combining Norm212 and my answer to make a  functional  solution   b    1 1 3  each with object  a      del  a delete at  a index  del         Put it in a lambda if needed   subtract   lambda do  minuend  subtrahend    subtrahend each with object  minuend      del  minuend delete at  minuend index  del       end   then   subtract call a   1 1 3

User · Answer

You may do   a   1 1 1 2 2 3  delete list    1 3  delete list each do  del      a delete at a index del   end   result    1  1  2  2

[ruby] Removing elements from array Ruby

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