问题
I am trying to create a column that does a cumulative sum using 2 columns , please see example of what I am trying to do :@Faith Akici
index lodgement_year words sum cum_sum
0 2000 the 14 14
1 2000 australia 10 10
2 2000 word 12 12
3 2000 brand 8 8
4 2000 fresh 5 5
5 2001 the 8 22
6 2001 australia 3 13
7 2001 banana 1 1
8 2001 brand 7 15
9 2001 fresh 1 6
I have used the code below , however my computer keep crashing , I am unsure if is the code or the computer. Any help will be greatly appreciated:
df_2['cumsum']= df_2.groupby('lodgement_year')['words'].transform(pd.Series.cumsum)
Update ; I have also used the code below , it worked and said exit code 0 . However with some warnings.
df_2['cum_sum'] =df_2.groupby(['words'])['count'].cumsum()
回答1:
You are almost there, Ian!
cumsum()
method calculates the cumulative sum of a Pandas column. You are looking for that applied to the grouped words
. Therefore:
In [303]: df_2['cumsum'] = df_2.groupby(['words'])['sum'].cumsum()
In [304]: df_2
Out[304]:
index lodgement_year words sum cum_sum cumsum
0 0 2000 the 14 14 14
1 1 2000 australia 10 10 10
2 2 2000 word 12 12 12
3 3 2000 brand 8 8 8
4 4 2000 fresh 5 5 5
5 5 2001 the 8 22 22
6 6 2001 australia 3 13 13
7 7 2001 banana 1 1 1
8 8 2001 brand 7 15 15
9 9 2001 fresh 1 6 6
Please comment if this fails on your bigger data set, and we'll work on a possibly more efficient version of this.
(And by the way, I didn't get a notification because you made a typo in my name: Fatih, not Faith :))
回答2:
If we only need to consider the column 'words', we might need to loop through unique values of the words
for unique_words in df_2.words.unique():
if 'cum_sum' not in df_2:
df_2['cum_sum'] = df_2.loc[df_2['words'] == unique_words]['sum'].cumsum()
else:
df_2.update(pd.DataFrame({'cum_sum': df_2.loc[df_2['words'] == unique_words]['sum'].cumsum()}))
above will result to:
>>> print(df_2)
lodgement_year sum words cum_sum
0 2000 14 the 14.0
1 2000 10 australia 10.0
2 2000 12 word 12.0
3 2000 8 brand 8.0
4 2000 5 fresh 5.0
5 2001 8 the 22.0
6 2001 3 australia 13.0
7 2001 1 banana 1.0
8 2001 7 brand 15.0
9 2001 1 fresh 6.0
来源:https://stackoverflow.com/questions/48033351/cumulative-sum-using-2-columns