Contents
Outline
In this blog post, we’ll see what the Iterator is, and how to use the Iterator to handle arrays easily.
Iterator
The Iterator is a method to iterate over each element of an object with multiple elements, such as an array. In this blog post, I will introduce the frequently used iterators.
each method
Each element of the array is assigned to |variable| and iterates over it.
<Array>.each { |<Variable>|
Repeat actions
}
You can use each method like below.
fruits = ['apple', 'banana', 'orange']
fruits.each {|fruit|
puts fruit
}
times method
If the number of iterations is fixed, you can use times method.
4.times {
puts 'Hello world'
}
In Ruby, the number is also an object, so you can use times method like above.
loop method
The loop method performs iteration without termination.
i = 0
loop {
i += 1
puts 'Hello world'
if i == 4
break
end
}
You can terminate loop by using break like above, but If you don’t, it will be into the infinite loop, so be careful to use this.
Iterators usage
When you handle the Arrays, it is more convenient to use iterators.
each_with_index method
If you need the Index in the Arrays, you can use each_with_index method.
fruits = ['apple', 'banana', 'orange']
fruits.each_with_index {|fruit, i|
puts "#{i}: #{fruit}"
}
Hash
You can also use the Iterators in Hash.
fruits = {:Apple => 'apple', :Banana => 'banana', :Orange => 'orange'}
fruits.each {|key, value|
puts "#{key}: #{value}"
}
File
You can use the Iterators in the File class. If you use the Iterator in the File, you can get the line of the text file.
file = File.open("test.txt")
file.each {|line|
puts line
}
file.close
Define the iterator
When you define the method, you can define the Iterator by using yield.
def temp
yield 10
yield 'Hello'
end
temp {|value|
puts value * 2
}
# 20
# HelloHello
Completed
We’ve seen what the iterator is, and how to use the iterator. Also, we can define a new iterator when we need. From now on, let’s use the Iterators to handle Arrays, Hash, and so on.
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