ale19 - 7 months ago 51

Python Question

Say I have a dataframe with two rows that have the same value:

`testdf = pd.DataFrame({'a': ['alpha','beta','theta','delta','epsilon'],'b':[1,2,3,3,4]})`

a b

0 alpha 1

1 beta 2

2 theta 3

3 delta 3

4 epsilon 4

Now I want to sort them based on column B:

`testdf['rank'] = testdf['b'].rank(ascending=False)`

a b rank

0 alpha 1 5.0

1 beta 2 4.0

2 theta 3 2.5

3 delta 3 2.5

4 epsilon 4 1.0

Since rows 2 and 3 have the same rank, I'd like to arrange them in alphabetical order for the viewer:

`a b rank`

0 alpha 1 5.0

1 beta 2 4.0

3 delta 3 2.5

2 theta 3 2.5

4 epsilon 4 1.0

But I'm not sure how to do this. Maybe I could group them by rank and order them...? I'm not sure how to do that in-place, though.

Answer

It's possible to sort by more than one column using `sort_values`

, what you want is to sort by `rank`

first, then by the `a`

column, and if you want it to happen inplace, we use `inplace=True`

like below:

```
In [14]: testdf.sort_values(['rank', 'a'], ascending=[False, True], inplace=True)
In [15]: testdf
Out[15]:
a b rank
0 alpha 1 5.0
1 beta 2 4.0
3 delta 3 2.5
2 theta 3 2.5
4 epsilon 4 1.0
```

Which is the result you want and inplace, if you don't use `inplace=True`

the resulting dataframe will be returned from the operation.