爲熊貓數據框中的行子集隨機賦值

Question

我使用Python 2.7.11和Anaconda。

我知道如何設置PandasDataFrame的行子集的值，如Modifying a subset of rows in a pandas dataframe，但我需要隨機設置這些值。

說我有下面的數據幀df。我如何隨機設置group == 2的值，使它們不都等於1.0？

import pandas as pd 
import numpy as np 

df = pd.DataFrame([1,1,1,2,2,2], columns = ['group']) 
df['value'] = np.nan 
df.loc[df['group'] == 2, 'value'] = np.random.randint(0,5) 

print df 
    group value 
0  1 NaN 
1  1 NaN 
2  1 NaN 
3  2 1.0 
4  2 1.0 
5  2 1.0 

df應該看起來像下面：

print df 
    group value 
0  1 NaN 
1  1 NaN 
2  1 NaN 
3  2 1.0 
4  2 4.0 
5  2 2.0 

Answer 1

您必須確定組的大小2

g2 = df['group'] == 2 
df.loc[g2, 'value'] = np.random.randint(5, size=g2.sum()) 
print(df) 

    group value 
0  1 NaN 
1  1 NaN 
2  1 NaN 
3  2 3.0 
4  2 4.0 
5  2 2.0