Shuffle a pandas dataframe by groups

问题

My dataframe looks like this

sampleID  col1 col2
   1        1   63
   1        2   23
   1        3   73
   2        1   20
   2        2   94
   2        3   99
   3        1   73
   3        2   56
   3        3   34

I need to shuffle the dataframe keeping same samples together and the order of the col1 must be same as in above dataframe.

So I need it like this

sampleID  col1 col2
   2        1   20
   2        2   94
   2        3   99
   3        1   73
   3        2   56
   3        3   34
   1        1   63
   1        2   23
   1        3   73

How can I do this? If my example is not clear please let me know.

回答1:

Assuming you want to shuffle by sampleID. First df.groupby, shuffle (import random first), and then call pd.concat:

import random

groups = [df for _, df in df.groupby('sampleID')]
random.shuffle(groups)

pd.concat(groups).reset_index(drop=True)

   sampleID  col1  col2
0         2     1    20
1         2     2    94
2         2     3    99
3         1     1    63
4         1     2    23
5         1     3    73
6         3     1    73
7         3     2    56
8         3     3    34

You reset the index with df.reset_index(drop=True), but it is an optional step.

回答2:

Just to add one thing to @cs95 answer. If you want to shuffle by sampleID but you want to have your sampleIDs ordered from 1. So here the sampleID is not that important to keep. Here is a solution where you have just to iterate over the gourped dataframes and change the sampleID.

groups = [df for _, df in df.groupby('doc_id')]

random.shuffle(groups)

for i, df in enumerate(groups):
     df['doc_id'] = i+1

shuffled = pd.concat(groups).reset_index(drop=True)

        doc_id  sent_id  word_id
   0       1        1       20
   1       1        2       94
   2       1        3       99
   3       2        1       63
   4       2        2       23
   5       2        3       73
   6       3        1       73
   7       3        2       56
   8       3        3       34

来源：https://stackoverflow.com/questions/45585860/shuffle-a-pandas-dataframe-by-groups

标签

python

pandas

dataframe

shuffle