Drop all duplicate rows across multiple columns in Python Pandas
PythonPandasDuplicatesDrop DuplicatesPython Problem Overview
The pandas drop_duplicates function is great for "uniquifying" a dataframe. However, one of the keyword arguments to pass is take_last=True or take_last=False, while I would like to drop all rows which are duplicates across a subset of columns. Is this possible?
A B C
0 foo 0 A
1 foo 1 A
2 foo 1 B
3 bar 1 A
As an example, I would like to drop rows which match on columns A and C so this should drop rows 0 and 1.
Python Solutions
Solution 1 - Python
This is much easier in pandas now with drop_duplicates and the keep parameter.
import pandas as pd
df = pd.DataFrame({"A":["foo", "foo", "foo", "bar"], "B":[0,1,1,1], "C":["A","A","B","A"]})
df.drop_duplicates(subset=['A', 'C'], keep=False)
Solution 2 - Python
Just want to add to Ben's answer on drop_duplicates:
keep : {‘first’, ‘last’, False}, default ‘first’
-
first : Drop duplicates except for the first occurrence.
-
last : Drop duplicates except for the last occurrence.
-
False : Drop all duplicates.
So setting keep to False will give you desired answer.
> DataFrame.drop_duplicates(*args, **kwargs) Return DataFrame with
> duplicate rows removed, optionally only considering certain columns
>
> Parameters: subset : column label or sequence of labels, optional
> Only consider certain columns for identifying duplicates, by default
> use all of the columns keep : {‘first’, ‘last’, False}, default
> ‘first’ first : Drop duplicates except for the first occurrence. last
> : Drop duplicates except for the last occurrence. False : Drop all
> duplicates. take_last : deprecated inplace : boolean, default False
> Whether to drop duplicates in place or to return a copy cols : kwargs
> only argument of subset [deprecated] Returns: deduplicated :
> DataFrame
Solution 3 - Python
If you want result to be stored in another dataset:
df.drop_duplicates(keep=False)
or
df.drop_duplicates(keep=False, inplace=False)
If same dataset needs to be updated:
df.drop_duplicates(keep=False, inplace=True)
Above examples will remove all duplicates and keep one, similar to DISTINCT * in SQL
Solution 4 - Python
use groupby and filter
import pandas as pd
df = pd.DataFrame({"A":["foo", "foo", "foo", "bar"], "B":[0,1,1,1], "C":["A","A","B","A"]})
df.groupby(["A", "C"]).filter(lambda df:df.shape[0] == 1)
Solution 5 - Python
Try these various things
df = pd.DataFrame({"A":["foo", "foo", "foo", "bar","foo"], "B":[0,1,1,1,1], "C":["A","A","B","A","A"]})
>>>df.drop_duplicates( "A" , keep='first')
or
>>>df.drop_duplicates( keep='first')
or
>>>df.drop_duplicates( keep='last')
Solution 6 - Python
Actually, drop rows 0 and 1 only requires (any observations containing matched A and C is kept.):
In [335]:
df['AC']=df.A+df.C
In [336]:
print df.drop_duplicates('C', take_last=True) #this dataset is a special case, in general, one may need to first drop_duplicates by 'c' and then by 'a'.
A B C AC
2 foo 1 B fooB
3 bar 1 A barA
[2 rows x 4 columns]
But I suspect what you really want is this (one observation containing matched A and C is kept.):
In [337]:
print df.drop_duplicates('AC')
A B C AC
0 foo 0 A fooA
2 foo 1 B fooB
3 bar 1 A barA
[3 rows x 4 columns]
#Edit: Now it is much clearer, therefore:
In [352]:
DG=df.groupby(['A', 'C'])
print pd.concat([DG.get_group(item) for item, value in DG.groups.items() if len(value)==1])
A B C
2 foo 1 B
3 bar 1 A
[2 rows x 3 columns]