How to do substruction in the cells of columns in python

Question

I have this dataframe (df) in python:

  Cumulative sales
0        12
1        28
2        56
3        87

I want to create a new column in which I whould have the the number of new sales (N-(N-1)) as below:

  Cumulative sales   New Sales
0        12             12
1        28             16
2        56             28
3        87             31

this is dupe of [this](https://stackoverflow.com/questions/13114512/calculating-difference-between-two-rows-in-python-pandas) or [this one](https://stackoverflow.com/questions/34846146/how-to-calculate-differences-between-consecutive-rows-in-pandas-data-frame) — Ben.T, May 19 '20 at 23:50
Does this answer your question? [Calculating difference between two rows in Python / Pandas](https://stackoverflow.com/questions/13114512/calculating-difference-between-two-rows-in-python-pandas) — mechanical_meat, May 19 '20 at 23:51

score 0 · Answer 1 · answered May 19 '20 at 23:51

Do this:

df['New_sales'] = df['Cumlative_sales'].diff()
df.fillna(df.iloc[0]['Cumlative_sales'], inplace=True)
print(df)

Output:

   Cumlative_sales  New_sales
0               12       12.0
1               28       16.0
2               56       28.0
3               87       31.0

score 0 · Accepted Answer · answered May 20 '20 at 00:03

0

You can do

df['new sale']=df.Cumulativesales.diff().fillna(df.Cumulativesales)
df
   Cumulativesales  new sale
0               12      12.0
1               28      16.0
2               56      28.0
3               87      31.0

answered May 20 '20 at 00:03

BENY

317,841
20
164
234

How to do substruction in the cells of columns in python

2 Answers2