python - 按字符串过滤，然后找到另一列的方差

Question

我使用 pandas 读取我的 csv 文件，然后只读取这两列

• 描述文件

• 数字

Describe_File   numbers
0   This is the start   25
1   Ending is coming    42
2   Middle of the story 525
3   This is the start   65
4   This is the start   25
5   Middle of the story 35
6   This is the start   28
7   This is the start   24
8   Ending is coming    24
9   Ending is coming    35
10  Ending is coming    25
11  Ending is coming    24
12  This is the start   215

所以我现在按字符串名称过滤 ** This is the start** 看起来像这样

df = df[df.Describe_File == "这是开始"]

    Describe_File   numbers
0   This is the start   25
3   This is the start   65
4   This is the start   25
6   This is the start   28
7   This is the start   24
12  This is the start   21

现在我只是找到方差np.var(df)

目标

转到 Describe_File 按所有唯一字符串进行过滤，然后找出该字符串的方差和标准差。

输出文件应该是这样的

Answer 1

如您所知，标准差是方差的平方根。所以以下将是最快的方法。

import pandas as pd
import numpy as np

df_out = df.groupby('Describe_File').apply(np.var)
df_out.columns = ['variance']
df_out['standard_deviation'] = np.sqrt(df_out['variance'])