Difference between map and collect in Ruby

Question

I have Googled this and got patchy   contradictory opinions - is there actually any difference between doing a map and doing a collect on an array in Ruby Rails    The docs don t seem to suggest any  but are there perhaps differences in method or performance

User · Answer

I did a benchmark test to try and answer this question, then found this post so here are my findings (which differ slightly from the other answers)

Here is the benchmark code:

require 'benchmark'

h = { abc: 'hello', 'another_key' => 123, 4567 => 'third' }
a = 1..10
many = 500_000

Benchmark.bm do |b|
  GC.start

  b.report("hash keys collect") do
    many.times do
      h.keys.collect(&:to_s)
    end
  end

  GC.start

  b.report("hash keys map") do
    many.times do
      h.keys.map(&:to_s)
    end
  end

  GC.start

  b.report("array collect") do
    many.times do
      a.collect(&:to_s)
    end
  end

  GC.start

  b.report("array map") do
    many.times do
      a.map(&:to_s)
    end
  end
end

And the results I got were:

                   user     system      total        real
hash keys collect  0.540000   0.000000   0.540000 (  0.570994)
hash keys map      0.500000   0.010000   0.510000 (  0.517126)
array collect      1.670000   0.020000   1.690000 (  1.731233)
array map          1.680000   0.020000   1.700000 (  1.744398)

Perhaps an alias isn't free?

User · Answer

There s no difference  in fact map is implemented in C as rb ary collect and enum collect  eg  there is a difference between map on an array and on any other enum  but no difference between map and collect      Why do both map and collect exist in Ruby  The map function has many naming conventions in different languages  Wikipedia provides an overview      The map function originated in functional programming languages but is today supported  or may be defined  in many procedural  object oriented  and multi-paradigm languages as well  In C   s Standard Template Library  it is called transform  in C   3 0  s LINQ library  it is provided as an extension method called Select  Map is also a frequently used operation in high level languages such as Perl  Python and Ruby  the operation is called map in all three of these languages  A collect alias for map is also provided in Ruby  from Smalltalk   emphasis mine   Common Lisp provides a family of map-like functions  the one corresponding to the behavior described here is called mapcar  -car indicating access using the CAR operation      Ruby provides an alias for programmers from the Smalltalk world to feel more at home     Why is there a different implementation for arrays and enums  An enum is a generalized iteration structure  which means that there is no way in which Ruby can predict what the next element can be  you can define infinite enums  see Prime for an example   Therefore it must call a function to get each successive element  typically this will be the each method     Arrays are the most common collection so it is reasonable to optimize their performance  Since Ruby knows a lot about how arrays work it doesn t have to call each but can only use simple pointer manipulation which is significantly faster   Similar optimizations exist for a number of Array methods like zip or count

User · Answer

I ve been told they are the same    Actually they are documented in the same place under ruby-doc org   http   www ruby-doc org core classes Array html M000249        ary collect   item  block     new ary   ary map   item  block     new ary   ary collect   an enumerator   ary map   an enumerator         Invokes block once for each element of self     Creates a new array containing the values returned by the block     See also Enumerable collect    If no block is given  an enumerator is returned instead   a      a    b    c    d    a collect   x  x              gt    a     b     c     d    a                             gt    a    b    c    d

User · Answer

The collect and collect  methods are aliases to map and map   so they can be used interchangeably  Here is an easy way to confirm that   Array instance method  map     Array instance method  collect     gt  true

User · Answer

Ruby aliases the method Array map to Array collect  they can be used interchangeably   Ruby Monk   In other words  same source code                   static VALUE rb ary collect VALUE ary    long i  VALUE collect   RETURN SIZED ENUMERATOR ary  0  0  ary enum length   collect   rb ary new2 RARRAY LEN ary    for  i   0  i  lt  RARRAY LEN ary   i          rb ary push collect  rb yield RARRAY AREF ary  i       return collect      http   ruby-doc org core-2 2 0 Array html method-i-map

User · Answer

collect is actually an alias for  map  That means the two methods can be used interchangeably  and effect the same behavior

[ruby] Difference between map and collect in Ruby?

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