How can I sort a file with pairs in reverse order?

[Pedro Sá da Costa]

I created a MapReduce job example that that uses the sort mechanism of
hadoop to sort a file by the key in ascending order. This is an example of
the data:

7    vim
2    emacs
9    firefox

At the end, I get the result:

2    emacs
7    vim
 9    firefox



Now I want to sort in reverse order, for the result be:
9    firefox
7    vim
2    emacs



How can I sort a file with pairs <Key Value> in reverse order?

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Best regards,