What is the difference between map, each, and collect?

ruby enumerable
Rahul picture Rahul · Feb 24, 2012 · Viewed 38.8k times · Source

In Ruby, is there any difference between the functionalities of each, map, and collect?

Answer

Chowlett picture Chowlett · Feb 24, 2012

each is different from map and collect, but map and collect are the same (technically map is an alias for collect, but in my experience map is used a lot more frequently).

each performs the enclosed block for each element in the (Enumerable) receiver:

[1,2,3,4].each {|n| puts n*2}
# Outputs:
# 2
# 4
# 6
# 8

map and collect produce a new Array containing the results of the block applied to each element of the receiver:

[1,2,3,4].map {|n| n*2}
# => [2,4,6,8]

There's also map! / collect! defined on Arrays; they modify the receiver in place:

a = [1,2,3,4]
a.map {|n| n*2} # => [2,4,6,8]
puts a.inspect  # prints: "[1,2,3,4]"
a.map! {|n| n+1}
puts a.inspect  # prints: "[2,3,4,5]"

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