how we can convert categorical data in a column into numbered data

Question

Lets take an example, suppose my table values are:

subjects

english

mathematics

science

english

science

how can i convert these string data into numbered data as shown in table below.

subjects

1

2

3

1

3

Answer 1

Assuming your original dataframe looks like this:

>>> df
      subjects
0      english
1  mathematics
2      science
3      english
4      science

you could use pd.factorize:

df['factor'] = pd.factorize(df['subjects'])[0]+1

>>> df
      subjects  factor
0      english       1
1  mathematics       2
2      science       3
3      english       1
4      science       3

or, if you simply want to replace the values in subjects rather than create a new column factor, do this:

df['subjects'] = pd.factorize(df['subjects'])[0]+1

Note that the +1 is simply to get your exact output ranging from 1 to 3. Without it, you will still get valid categories, only ranging from 0 to 2.