使用 pandas 从每个组中随机选择一行 [英] Randomly select a row from each group using pandas

问题描述

我有一个熊猫数据框df，它显示如下:

I have a pandas dataframe df which appears as following:

Month   Day mnthShape
1      1    1.016754224
1      1    1.099451003
1      1    0.963911929
1      2    1.016754224
1      1    1.099451003
1      2    0.963911929
1      3    1.016754224
1      3    1.099451003
1      3    1.783775568

我想从df中获得以下信息:

I want to get the following from df:

Month   Day mnthShape
1       1   1.016754224
1       2   1.016754224
1       3   1.099451003

其中，mnthShape值是从索引中随机选择的.也就是说，如果查询为df.loc [(1，1)]，则应查找(1，1)的所有值，然后从中随机选择一个要在上方显示的值.

where the mnthShape values are selected at random from the index. i.e. if the query is df.loc[(1, 1)] it should look for all values for (1, 1) and select randomly from it a value to be displayed above.

推荐答案

使用groupby和apply在每个组中随机选择一行.

Use groupby with apply to select a row at random per group.

np.random.seed(0)
df.groupby(['Month', 'Day'])['mnthShape'].apply(np.random.choice).reset_index()

   Month  Day  mnthShape
0      1    1   1.016754
1      1    2   0.963912
2      1    3   1.099451

如果您想知道采样行来自哪个索引，请将pd.Series.sample与n=1结合使用:

If you want to know what index the sampled rows come from, use pd.Series.sample with n=1:

np.random.seed(0)
(df.groupby(['Month', 'Day'])['mnthShape']
   .apply(pd.Series.sample, n=1)
   .reset_index(level=[0, 1]))

   Month  Day  mnthShape
2      1    1   0.963912
3      1    2   1.016754
6      1    3   1.016754

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