invert() public

Returns a new hash created by using hsh’s values as keys, and the keys as values. If a key with the same value already exists in the hsh, then the last one defined will be used, the earlier value(s) will be discarded.

h = { "n" => 100, "m" => 100, "y" => 300, "d" => 200, "a" => 0 }
h.invert   #=> {0=>"a", 100=>"m", 200=>"d", 300=>"y"}

If there is no key with the same value, Hash#invert is involutive.

h = { a: 1, b: 3, c: 4 }
h.invert.invert == h #=> true

The condition, no key with the same value, can be tested by comparing the size of inverted hash.

# no key with the same value
h = { a: 1, b: 3, c: 4 }
h.size == h.invert.size #=> true

# two (or more) keys has the same value
h = { a: 1, b: 3, c: 1 }
h.size == h.invert.size #=> false
Show source
Register or log in to add new notes.