counting the number of occurences in a file of data list

Question

I have a data file, like

7
2
10
9
10
3
2
4
2
4
6

Each line has a single value. I want to count the occurence of each value. For instance, 10 occurs two times in this file.

Is there a simple way to do that under linux without writing formal counting program?

Answer 1

Yes, there is:

$ sort -n file | uniq -c

Where -n enables numeric sorting and -c enables counting.

For the above sequence:

$ echo -e '7\n2\n10\n9\n10\n3\n2\n4\n2\n4\n6' | sort -n | uniq -c 
  3 2
  1 3
  2 4
  1 6
  1 7
  1 9
  2 10

(The first columns contains the counts, the 2nd the numbers.)