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"            #=> 5 a.count "lo", "o"       #=> 2 a.count "hello", "^l"   #=> 4 a.count "ej-m"          #=> 4 

Any explanation will be helpful.

Answer 1

This is one of the dorkiest ruby methods, and pretty lousy documentation to boot. Threw me for a loop. I ended up looking at it because it looked like it should give me the count of occurrences of a given string. Nope. Not remotely close. But here is how I ended up counting string occurrences:

s="this is a string with is thrice" s.scan(/is/).count  # => 3 

Makes me wonder why someone asked for this method, and why the documentation is so lousy. Almost like the person documenting the code really did not have a clue as to the human-understandable "business" reason for asking for this feature.

count([other_str]+) → fixnum

Each _other_str_ parameter defines a set of characters to count. The intersection of these sets defines the characters to count in str. Any _other_str_ that starts with a caret (^) is negated. The sequence c1–c2 means all characters between c1 and c2.

Answer 2

If you pass more than 1 parameter to count, it will use the intersection of those strings and will use that as the search target:

a = "hello world" a.count "lo"            #=> finds 5 instances of either "l" or "o" a.count "lo", "o"       #=> the intersection of "lo" and "o" is "o", so it finds 2 instances a.count "hello", "^l"   #=> the intersection of "hello" and "everything that is not "l" finds 4 instances of either "h", "e" or "o" a.count "ej-m"          #=> finds 4 instances of "e", "j", "k", "l" or "m" (the "j-m" part)