熊猫groupby筛选器，删除一些组

Question

I have groupby object

grouped = df.groupby('name')
for k,group in grouped:    
    print group

there are 3 groups bar , foo and foobar

  name  time  
2  bar     5  
3  bar     6  


  name  time  
0  foo     5  
1  foo     2  

  name      time  
4  foobar     20  
5  foobar     1  

I need to filter these groups and drop all groups which have no time greater than 5. In my example the group foo should be dropped. I am trying to do it with function filter()

grouped.filter(lambda x: (x.max()['time']>5))

but the x is obviously not only the group in dataframe format.

Answer 1

Assuming your final line of code really should have a >5 rather than >20 , you would do something similar to:

grouped.filter(lambda x: (x.time > 5).any())

As you correctly spotted x is actually a DataFrame for all indices where the name column matches the key you have in k in your for-loop.

So you want to filter based on if there are any times larger than 5 in the time-column you do the above (x.time > 5).any() to test it.

Answer 2

I'm not used to python, numpy or pandas yet. But I was investigating a solution to a similar problem, so let me report my answers by taking this question as an example.

import pandas as pd

df = pd.DataFrame()
df['name'] = ['foo', 'foo', 'bar', 'bar', 'foobar', 'foobar']
df['time'] = [5, 2, 5, 6, 20, 1]

grouped = df.groupby('name')
for k, group in grouped:
    print(group)

My Answer 1:

indexes_should_drop = grouped.filter(lambda x: (x['time'].max() <= 5)).index
result1 = df.drop(index=indexes_should_drop)

My Answer 2:

filter_time_max = grouped['time'].max() > 5
groups_should_keep = filter_time_max.loc[filter_time_max].index
result2 = df.loc[df['name'].isin(groups_should_keep)]

My Answer 3:

filter_time_max = grouped['time'].max() <= 5
groups_should_drop = filter_time_max.loc[filter_time_max].index
result3 = df.drop(df[df['name'].isin(groups_should_drop)].index)

Results

    name    time
2   bar     5
3   bar     6
4   foobar  20
5   foobar  1

Points

My Answer1 doesn't use group names to drop groups. If you need group names, you can get them by writing: df.loc[indexes_should_drop].name.unique() .

grouped['time'].max() <= 5 and grouped.apply(lambda x: (x['time'].max() <= 5)).index returned same results.

filter_time_max 's index was a group name. It could not be used as an index or label to drop as it is.

name
foo        True
bar       False
foobar    False
Name: time, dtype: bool