String#count options

Question

From the documentation for String#count I understand the first example, but I do not understand the rest of the examples:

a = \"hello world\"
a.count \"lo\"              


        

Answer 1

Let's break these down

a = "hello world"

1. to count the number of occurrences of the letters l and o

   a.count "lo" #=> 5

2. to find the intersect of lo and o (which is counting the number of occurrences of l and o and taking only the count of o from the occurrences):

   a.count "lo", "o" #=> 2

3. to count the number of occurrences of h, e, l, l and o, then intersect with any that are not l (which produces the same outcome to finding occurrences of h, e and o)

   a.count "hello", "^l" #=> 4

4. to count the number of occurrences of e and any letter between j and m (j, k, l and m):

   a.count "ej-m" #=> 4