Ruby: Map Function to List

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Map Function to List

Use ‹array›.map {…} method on array object to create a new array. Example:

# -*- coding: utf-8 -*-
# ruby

def ff(n)
 n*n
end

aa = 0..4                       # array 0 to 4

p aa.map {|xx| ff xx}           # ⇒ [0, 1, 4, 9, 16]

Use method ‹array›.map! {…} to have the original array modified.

Removing Elements in a List

To remove elements, use “select” method and pass it a block.

In Ruby, many methods can take a “block” argument. The “block” is a kind of lambda expression. The syntax has the form: ‹object name›.‹method name› { |‹x›| ‹expression on x›}. Example:

# -*- coding: utf-8 -*-
# ruby

aa = 0..10                      # a array 0 to 10

p aa.select { |xx| xx % 2 == 0 }   # ⇒ [0, 2, 4, 6, 8, 10]
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