Question

import numpy as np
import panda as pd

dates = pd.date_range('20161104', periods = 10)
df = pd.DataFrame(np.random.randn(10, 4), index = dates, columns = list('ABCD'))

当C大于0时，我试图找到A的平均值，这意味着如果相应的C小于0，我将不计算A进入我的计算。

有没有人知道如何在不创建新数据集或使用groupby的情况下制作它？谢谢！

Answer 1

你可以试试这个：

df[df.C> 0]['A'].mean()

Answer 2

我不确定究竟需要什么：

np.random.seed(1)
dates = pd.date_range('20161104', periods = 10)
df = pd.DataFrame(np.random.randn(10, 4), index = dates, columns = list('ABCD'))
print (df)
                   A         B         C         D
2016-11-04  1.624345 -0.611756 -0.528172 -1.072969
2016-11-05  0.865408 -2.301539  1.744812 -0.761207
2016-11-06  0.319039 -0.249370  1.462108 -2.060141
2016-11-07 -0.322417 -0.384054  1.133769 -1.099891
2016-11-08 -0.172428 -0.877858  0.042214  0.582815
2016-11-09 -1.100619  1.144724  0.901591  0.502494
2016-11-10  0.900856 -0.683728 -0.122890 -0.935769
2016-11-11 -0.267888  0.530355 -0.691661 -0.396754
2016-11-12 -0.687173 -0.845206 -0.671246 -0.012665
2016-11-13 -1.117310  0.234416  1.659802  0.742044

#mean of A where C is larger than 0
print (df.ix[df.C > 0, 'A'].mean())
-0.2547213686717275

#mean of A where C is less than 0
print (df.ix[df.C < 0, 'A'].mean())
0.3925351332955095

#mean of A where C is larger than 0 and C is less than 0, co condition never return True
print (df.ix[(df.C > 0) & (df.C < 0), 'A'].mean())
nan

#mean of A where A is larger than 0 and C is less than 0
print (df.ix[(df.A > 0) & (df.C < 0), 'A'].mean())
1.2626006564638268

如何使用dataFrame查找一组数据的平均值？

2 个答案: