I want to transform the short repeated words in columns into numbers.

In the following example I want to change the words `(with ONLY 2 LETTERS)` in column 3 for numbers, so that `AA` is changed to `2`, `AB` or `BA` into `1`, `BB` into `0`.

The first and second column may also contain `AA`, `BB`, `AB` and `BA`. These should not be changed.

Columns are separated by `" "` ().

```
Id_animal Id_SNP Allele
ID01 rs01 AB
ID02 rs01 BA
ID03 rs01 AA
ID04 rs01 BB

```

The wanted output is:

```
Id_animal Id_SNP Allele
ID01 rs01 1
ID02 rs01 1
ID03 rs01 2
ID04 rs01 0

```