Python:在计数条件下删除行 [英] Python: Removing Rows on Count condition

问题描述

我在过滤pandas数据帧时遇到问题.

I have a problem filtering a pandas dataframe.

city 
NYC 
NYC 
NYC 
NYC 
SYD 
SYD 
SEL 
SEL
...

df.city.value_counts()

我想删除计数频率低于4的城市行，例如SYD和SEL.

I would like to remove rows of cities that has less than 4 count frequency, which would be SYD and SEL for instance.

如果不按城市逐个手动删除它们，该怎么办?

What would be the way to do so without manually dropping them city by city?

推荐答案

在这里使用过滤器

df.groupby('city').filter(lambda x : len(x)>3)
Out[1743]: 
  city
0  NYC
1  NYC
2  NYC
3  NYC

解决方案二transform

sub_df = df[df.groupby('city').city.transform('count')>3].copy() 
# add copy for future warning when you need to modify the sub df

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