[RAILS] [Ruby] From the basics to the inject method

inject method

Reference: https://docs.ruby-lang.org/ja/latest/method/Enumerable/i/inject.html

What is Enumerable in the first place?

module. A mix-in for repeating classes. The following are famous friends (instance methods).

Reference: https://docs.ruby-lang.org/ja/latest/class/Enumerable.html

In Ruby, thanks to the ʻEnumerable` module, you can use methods with convenient iterations.

Basic usage

ary = [1,2,3,4,5]
ary.inject(1){ |sum, n| sum + n }
# => 16

--The return value of each process in the block is in sum. --The method argument goes into the initial value (the block argument of the first process). --Repeat until the last element, and the return value of the last block becomes the total return value.

,,,Hard to understand.

Let's make it easy to understand.

ary = [1,2,3,4,5]
ary.inject(1) do |sum, n| 
  puts sum
  sum + n 
=>1 (Initial value specified in the argument of inject"1"Enters sum)
=>2 (Initial value (sum)+Sum of the first element (n) of the array)
=>4 (The return value (2) of the previous process is in sum+Second element sum)
=>7 (Omitted below)
=>16 (overall return value)

Can you imagine it somehow? This is ** folding **.

By the way, if you omit the method argument (hoge part of ʻinject (hoge)`), the first element of the array will be set to the initial value.

ary = [1,2,3,4,5]
ary.inject do |sum, n| 
  puts sum
  sum + n 
=>15 (overall return value)

What makes me happy

With a proper understanding, you can write complex processes in an easy-to-understand manner. Since the processing inside the block can be repeated by folding, it can be written shorter than the ʻeach` method.

In other words, it is often used for refactoring iterations.

Let's write some practical code below.

Actual usage

Get the sum of the arrays

For each

sum = 0
ary = [100,200,300,42,52]
ary.each { |n| sum += n }
puts sum
# =>694

In case of inject

ary = [100,200,300,42,52]
sum = ary.inject { |s, n| s += n }
puts sum
# =>694

One line has decreased. Refreshing.

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