### Question :

Convert pandas series from string to unique int ids [duplicate]

I have a categorical variable in a series. I want to assign integer ids to each unique value and create a new series with the ids, effectively turning a string variable into an integer variable. What is the most compact/efficient way to do this?

##
Answer #1:

You could use pandas.factorize:

```
In [32]: s = pd.Series(['a','b','c'])
In [33]: labels, levels = pd.factorize(s)
In [35]: labels
Out[35]: array([0, 1, 2])
```

##
Answer #2:

Example using the new pandas `categorical`

type in pandas 0.15+

http://pandas.pydata.org/pandas-docs/version/0.16.2/categorical.html

```
In [553]: x = pd.Series(['a', 'a', 'a', 'b', 'b', 'c']).astype('category')
In [554]: x
Out[554]:
0 a
1 a
2 a
3 b
4 b
5 c
dtype: category
Categories (3, object): [
a
, b
, c]
In [555]: x.cat.codes
Out[555]:
0 0
1 0
2 0
3 1
4 1
5 2
dtype: int8
```