Ruby Flatten Vs. Flat Map

Flatten will flatten all elements into a single array- flat map will only flatten one level, and retain nested arrays

#flatten flattens everything by default (retuning an array with no arrays as members), where #flat_map does not (if you pass it a multi-level array, it will retain the structure of it).

[1, [2,3],4,5  Private or Broken Links
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  ].flat_map {|i| i}
=> [1,2,3,[4,5]]
[1, [2,3],4,5  Private or Broken Links
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  ].map{|i| i}.flatten
=> [1,2,3,4,5]