Counting regex pattern matches in one line using sed or grep?

Question

I want to count the number of matches there is on one single line (or all lines as there always will be only one line).

I want to count not just one match per line as in

Answer 1

Maybe you should convert spaces to newlines first:

$ echo "1 1 2 2 2 5" | tr ' ' $'\n' | grep -c 2
3