What is the difference between map, each, and collect? [duplicate]

Answer 1

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]"

Answer 2

Each will evaluate the block but throws away the result of Each block's evaluation and returns the original array.

irb(main):> [1,2,3].each {|x| x*2}
=> [1, 2, 3]

Map/collect return an array constructed as the result of calling the block for each item in the array.

irb(main):> [1,2,3].collect {|x| x*2}
=> [2, 4, 6]