pandas dataframe delete groups with more than n rows in groupby

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I have a dataframe:

df = [type1 , type2 , type3 , val1, val2, val3
       a       b        q       1    2     3
       a       c        w       3    5     2
       b       c        t       2    9     0
       a       b        p       4    6     7
       a       c        m       2    1     8
       a       b        h       8    6     3
       a       b        e       4    2     7]

I want to apply groupby based on columns type1, type2 and delete from the dataframe the groups with more than 2 rows. So the new dataframe will be:

df = [type1 , type2 , type3 , val1, val2, val3
       a       c        w       3    5     2
       b       c        t       2    9     0
       a       c        m       2    1     8
  ]

What is the best way to do so?

pandas-groupby pandas dataframe python
1 Answers

Use GroupBy.transform for get counts of groups for Series with same size like original, so possible filter by Series.le for <= in boolean indexing:

df = df[df.groupby(['type1','type2'])['type1'].transform('size').le(2)]
print (df)
  type1 type2 type3  val1  val2  val3
1     a     c     w     3     5     2
2     b     c     t     2     9     0
4     a     c     m     2     1     8

If performace is not important or small DataFrame is possible use DataFrameGroupBy.filter:

df =df.groupby(['type1','type2']).filter(lambda x: len(x) <= 2)
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