Difference between collect, select, map and each in ruby

This post is not related to rails part but the RUBY part.

To iterate over an array we generally use collect, select, map and each. As I am beginner I never actually thought what is the difference and I kept using EACH for every loop iteration. However, recently I researched a bit more about these loops and thought to share it . It might help some one I guess  :)

1) Map

Map takes the enumerable object and a block like this [1,2,3].map { |n| n*2 } and evaluates the block for each element and then return a new array with the calculated values.

so the outcome of  [1,2,3].map { |n| n*2 } will be [2,4,6]

If you are try to use map to select any specific values like where n >2 then it will evaluate each element and will output only the result which will be either true or false

so the outcome of  [1,2,3].map { |n| n>2 } will be [false, false, true]

2) Collect

Collect is similar to Map which takes the enumerable object and a block like this [1,2,3].collect { |n| n*2 } and evaluates the block for each element and then return a new array with the calculated values.

so the outcome [1,2,3].collect{ |n| n*2 } of will be [2,4,6]

If you are try to use collect to select any specific values like where n >2 then it will evaluate each element and will output only the result which will be either true or false

so the outcome of  [1,2,3].collect { |n| n>2 } will be [false, false, true]

3) Select

Select evaluates the block with each element for which the block returns true.

so the outcome of  [1,2,3].select { |n| n*2 } will be [1,2,3]

If you are try to use select to get any specific values like where n >2 then it will evaluate each element but returns the array that meets the condition

so the outcome of  [1,2,3].select{ |n| n>2 } will be [3]

4) Each

Each will evaluate the block with each array and will return the original array not the calculated one.

so the outcome of  [1,2,3].each{ |n| n*2 } will be [1,2,3]

If you are try to use each to select any specific values like where n >2 then it will evaluate each element but returns the original array

so the outcome of  [1,2,3].each { |n| n>2 } will be [1,2,3]