2

Say we have a dataframe like this and want to remove columns when certain conditions met.

    df = pd.DataFrame(
np.arange(2, 14).reshape(-1, 4),
index=list('ABC'),
columns=pd.MultiIndex.from_arrays([
    ['data1', 'data2','data1','data2'],
    ['F', 'K','R','X'],
    ['C', 'D','E','E']
], names=['meter', 'Sleeper','sweeper'])
)

df

enter image description here

then lets say we want to remove cols only when meter == data1 and sweeper == E so I tried

df = df.drop(('data1','E'),axis = 1)

KeyError: 'E'

second try

df.drop(('data1','E'), axis = 1, level = 2)

KeyError: "labels [('data1', 'E')] not found in level"

Pandas: drop a level from a multi-level column index?

Alexander
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2 Answers2

2

Seems drop doesn't support selection over split levels ([0,2] here). We can create a mask with the conditions instead using get_level_values:

# keep where not ((level0 is 'data1') and (level2 is 'E'))
col_mask = ~((df.columns.get_level_values(0) == 'data1')
             & (df.columns.get_level_values(2) == 'E'))
df = df.loc[:, col_mask]

We can also do this by integer location by excluding the locs that are in a particular index slice, however, this is overall less clear and less flexible:

idx = pd.IndexSlice['data1', :, 'E']
cols = [i for i in range(len(df.columns))
        if i not in df.columns.get_locs(idx)]
df = df.iloc[:, cols]

Either approach produces df:

meter   data1 data2    
Sleeper     F     K   X
sweeper     C     D   E
A           2     3   5
B           6     7   9
C          10    11  13
Henry Ecker
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1

You have to do them individually, since they are on different levels:

df.drop('data1', axis=1, level='meter').drop('E', axis = 1, level='sweeper')
Out[833]: 
meter   data2
Sleeper     K
sweeper     D
A           3
B           7
C          11
sammywemmy
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