explain `.sum(0, &cols.method(:[])).to_i` in ruby

In Ruby, .sum(0, &cols.method(:[])).to_i is a method chaining expression used to calculate the sum of elements in an array.

Let's break it down step by step:

1. cols is an array or collection with multiple elements.
2. cols.method(:[]) is a way to get a reference to the [] method of the cols object. This method is used to access elements from the array.
3. The & operator is used to convert the method reference into a block.
4. .sum(0, &cols.method(:[])) calls the sum method on the array cols, passing two arguments: 0 and the block created from cols.method(:[]). The 0 argument is the initial value of the sum.
5. The sum method iterates over the elements in the array and sums them up, using the provided block (cols.method(:[])) to access each element.
6. .to_i converts the final sum value to an integer.

Overall, the expression .sum(0, &cols.method(:[])).to_i calculates the sum of elements in the cols array, by accessing each element in the array using the [] method, starting with an initial sum value of 0, and then converts the final sum to an integer.

Note that this expression assumes that cols is an array of numerical values.