I have a dataframe with multilabels as below:

```
 text   label
0   apple   a
1   apple   b
2   orange  o
3   orange  o
4   grapes  o
5   grapes  g

```

Expected output:

```
text    label
0   apple   ab
1   orange  o
2   orange  o
3   grapes  og

```

I tried df.groupby('label')['text']=='apple' but fail.
I tried df[(df.label=='a') & (df.label=='b')] which also fail.
How to select and rename the labels?