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how to drop duplicate rows in pandas



I have duplicate rows in data, let's say  'b' is the unique Id of the table

df = pd.DataFrame({
    'a': [1,2,3,4,5, 5, 5], 
    'b': ['a', 'e', 'b', 'c', 'd', 'd', 'd'], 
    'c': [False, True, True, False, True, True, True], 
    'd': [2006, 2006, 2007, 2008, 2006, 2006, 2007]

  a b c d
0 1 a False 2006
1 2 e True 2006
2 3 b True 2007
3 4 c False 2008
4 5 d True 2006
5 5 d True 2006
6 5 d True 2007


In the above data, row 4,5, 6 are similar. row 4 & 5 are exactly similar so if i use  "df.drop_duplicates()"  either 4 or 5 is removed but 6 is not removed because column 'd' has different values. So should I:

a) drop column 'd' and then run "df.drop_duplicates()", this way will loose column 'd' or

b) should I create another column and concatenate the values in column 'd' as '2006|2007' and then run "df.drop_duplicates()". This seems resonable but I dont know how to concatenate column values from two similar rows? Can you please help.

Or is there is better way to acheive such kind of duplicate data?

1 Answer(s)


By definition of duplicates, only row index 4 and 5 are duplicates. However snce you need to find duplicates as per only column b and c, you can perform a groupby on b and c and then convert the rows that you get as a single row.


Here are some alternatives based on what you need. Check the difference in the column d to understand what is happening. (Also note that you lose the relavance of the index).


df.groupby(['b', 'c']).max().reset_index()
df.groupby(['b', 'c']).min().reset_index()
group_cols = ['b', 'c']
other_cols = [c for c in df.columns if c not in group_cols]
df.groupby(group_cols).apply(lambda d: d[other_cols].apply(lambda var2: '|'.join([str(v) for v in var2.value_counts().index])))

Does this help you?

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