jerry_sjtu - 7 months ago 51

Python Question

Here is my code to generate a dataframe:

`import pandas as pd`

dff = pd.DataFrame(np.random.randn(1,2),columns=list('AB'))

then I got the dataframe:

`+------------+---------+--------+`

| | A | B |

+------------+---------+---------

| 0 | 0.626386| 1.52325|

+------------+---------+--------+

When I type the commmand :

`dff.mean(axis=1)`

I got :

`0 1.074821`

dtype: float64

According to the reference of pandas, axis=1 stands for columns and I expect the result of the command to be

`A 0.626386`

B 1.523255

dtype: float64

So here is my question: what does axis in pandas mean?

Answer

It specifies the axis **along which** the means are computed. By default `axis=0`

. This is consistent with the `numpy.mean`

usage when `axis`

is specified *explicitly* (in `numpy.mean`

, axis==None by default, which computes the mean value over the flattened array) , in which `axis=0`

along the *rows* (namely, *index* in pandas), and `axis=1`

along the *columns*.

```
+------------+---------+--------+
| | A | B |
+------------+---------+---------
| 0 | 0.626386| 1.52325|----axis=1----->
+------------+---------+--------+
| |
| axis=0 |
↓ ↓
```