How to order categorical string features in order of severity?

Question

If one of the features for my data set is a score that is categorical string like:

Score
X1c
X3a
X1a
X2b
X4
X1a
X1b
X4

Where X1a is the weakest followed by X1b, X1c, X2a, X2b ...X4 with X4 being the strongest, how can I encode it to integers such that X1a can be the lowest int and X4 be the highest int. I'm looking to use a random forest classifier. Also, the training set is a separate data set so this encoding should be maintained for new data sets.

Answer 1

You can try using rank:

df['Score_int'] = df.Score.rank(method='dense')

Output:

  Score  Score_int
0   X1c        3.0
1   X3a        5.0
2   X1a        1.0
3   X2b        4.0
4    X4        6.0
5   X1a        1.0
6   X1b        2.0
7    X4        6.0