Summing Collections

Given a hash, my_hash,

my_hash = {
    "one" => 1,
    "two" => 2,
    "three" => 5
}

I want to determine the sum of the values in my_hash, which should be 8.

This is similar to asking for the sum of the values in an array. In fact, using #values on my_hash will leave us with the task of summing the values in an array.

It turns out that to sum the values in an array, all you need is #inject

[1,2,5].inject(:+)
=> 8

So, if I want the sum of the values in a hash, such as my_hash, then all that is needed is

my_hash.values.inject(:+)
=> 8

To take this one step further, let's consider what will happen with an empty array. The above approach will produce nil. If we want 0 when the list is empty, then tell #inject to do just that

[].inject(0, :+)
=> 0

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