ruby: how to find non-unique elements in array and print each with number of occurrences?

Question

I have

a = [\"a\", \"d\", \"c\", \"b\", \"b\", \"c\", \"c\"]

and need to print something like (sorted descending by number of occurrences)

Answer 1

From Ruby 2.7, you can utilise Enumerable#tally and numbered block arguments:

a = ["a", "d", "c", "b", "b", "c", "c"]
puts a.tally.filter { _2 > 1 }.sort_by { -_2 }.map &:first

Here, Enumerable#tally returns a hash like { 'a' => 1, 'b' => 2, ... }, which you then have to filter and sort. After sorting, the hash would've collapsed to a nested array, e.g. [['b', 2], ...]. The last step is to take the first argument of each array element, using &:first.