jerry_sjtu jerry_sjtu - 4 months ago 15
Python Question

What does axis in pandas mean?

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  |
                ↓         ↓
Comments