Need a simple explanation of the inject method

Question

[1, 2, 3, 4].inject(0) { |result, element| result + element } # => 10

I\'m looking at this code but my brain is not registering how the number 1

Answer 1

What they said, but note also that you do not always need to provide a "starting value":

[1, 2, 3, 4].inject(0) { |result, element| result + element } # => 10

is the same as

[1, 2, 3, 4].inject { |result, element| result + element } # => 10

Try it, I'll wait.

When no argument is passed to inject, the first two elements are passed into the first iteration. In the example above, result is 1 and element is 2 the first time around, so one less call is made to the block.

Answer 2

This code doesn't allow the possibility of not passing a starting value, but may help explain what's going on.

def incomplete_inject(enumerable, result)
  enumerable.each do |item|
    result = yield(result, item)
  end
  result
end

incomplete_inject([1,2,3,4], 0) {|result, item| result + item} # => 10

Answer 3

The syntax for the inject method is as follows:

inject (value_initial) { |result_memo, object| block }

Let's solve the above example i.e.

[1, 2, 3, 4].inject(0) { |result, element| result + element }

which gives the 10 as the output.

So, before starting let's see what are the values stored in each variables:

result = 0 The zero came from inject(value) which is 0

element = 1 It is first element of the array.

Okey!!! So, let's start understanding the above example

Step :1 [1, 2, 3, 4].inject(0) { |0, 1| 0 + 1 }

Step :2 [1, 2, 3, 4].inject(0) { |1, 2| 1 + 2 }

Step :3 [1, 2, 3, 4].inject(0) { |3, 3| 3 + 3 }

Step :4 [1, 2, 3, 4].inject(0) { |6, 4| 6 + 4 }

Step :5 [1, 2, 3, 4].inject(0) { |10, Now no elements left in the array, so it'll return 10 from this step| }

Here Bold-Italic values are elements fetch from array and the simply Bold values are the resultant values.

I hope that you understand the working of the #inject method of the #ruby.

Answer 4

Inject applies the block

result + element

to each item in the array. For the next item ("element"), the value returned from the block is "result". The way you've called it (with a parameter), "result" starts with the value of that parameter. So the effect is adding the elements up.