Since it is a super-basic content, I think that it does not depend on the execution environment, but I will specify it for the time being. OS : macOS Catalina ver10.15.5 Ruby : 2.7.1p83
each
Basic iterative processing. The elements are taken out one by one and processed. Basically, it is surrounded by do ~ end. Pay attention to the scope of variables.
sample.rb
numbers = [1, 2, 4, 5, 6]
total = 0
numbers.each do |num|
total += num
end
p total　# 18
map
The feature is that it returns an array. The following processing adds 10 to the element and outputs it. For simple processing, you can enter with {} instead of do ~ end.
sample.rb
numbers = [1, 2, 4, 5, 6]
nuadd_num = numbers.map {|num| num + 10}
p add_num
# [11, 12, 14, 15, 16]
select
The values that match the judgment in the process are returned as an array.
sample.rb
numbers = [1, 2, 4, 5, 6]
numbers2 = numbers.select {|num| num % 2 == 0}
p numbers2
# [2, 4, 6]
reject
Values that do not match the judgment in the process are returned as an array. The opposite of select.
sample.rb
numbers = [1, 2, 4, 5, 6]
numbers2 = numbers.reject {|num| num % 2 == 0}
p numbers2
# [1, 5]
inject Folding process. Elements are assigned to num and i, respectively, and processing is performed.
sample.rb
numbers = [1, 2, 4, 5, 6]
numbers2 = numbers.inject {|num, i| num + i}
#1st loop num= 1, i = 2
#Second loop num= 3, i = 4
#3rd loop num= 7, i = 5
#4th loop num= 12, i = 6
p numbers2
# 18
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