count

        # Range.count

(from ruby core)
---
    count -> integer
    count(object) -> integer
    count {|element| ... } -> integer

---

Returns the count of elements, based on an argument or block criterion,
if given.

With no argument and no block given, returns the number of elements:

    (1..4).count      # => 4
    (1...4).count     # => 3
    ('a'..'d').count  # => 4
    ('a'...'d').count # => 3
    (1..).count       # => Infinity
    (..4).count       # => Infinity

With argument `object`, returns the number of `object` found in `self`,
which will usually be zero or one:

    (1..4).count(2)   # => 1
    (1..4).count(5)   # => 0
    (1..4).count('a')  # => 0

With a block given, calls the block with each element; returns the
number of elements for which the block returns a truthy value:

    (1..4).count {|element| element < 3 } # => 2

Related: Range#size.