Method count returns an integer count of the number of items in a collection that match a given criterion.

The method is available as:

• Array#count.
• Range#count.
• String#count (with a special implementation that is not discussed here).
• Enumerable#count, which is included or extended in a number of classes in the Ruby core and standard library.

There are three ways to call the method:

• With no argument and no block, returns the count of items in the collection:

[0, 1, 2].count # => 3
[].count # => 0

• With argument object, returns the count of items == object in the collection:

[0, 1, 2, 0.0].count(0) # => 2
[0, 1, 2].count(3) # => 0

• With a block, calls the block with each item in the collection; returns the count of elements for which the block returns a truthy value:

[0, 1, 2, 3].count {|element| element > 1} # => 2

More methods at #rubymethodoftheday.