Add Subsequent Values in Pandas Dataframe-CodePudding

I have the following dataframe:

Week Total
1     5
2     6
3     10

I want to make Week 2 equal to week1 week2, Week 3 equal to week1 week 2 week 3. My dataframe is bigger than this so simply doing additions doesn't work as the number of weeks can change dynamically. I honestly have no clue how to approach this. I was thinking maybe doing a for loop that iterates every week and subtracts the lowest week number from current to know how many weeks it needs to add. But it doesn't sound like a clean approach. Is there a better solution?

CodePudding user response：

Use a cumsum after sorting the rows by Week (if needed):

out = (df
  .sort_values('Week')
  .assign(Total=lambda d: d['Total'].cumsum())
)

If the weeks are already sorted:

df['Total'] = df['Total'].cumsum()

output:

   Week  Total
0     1      5
1     2     11
2     3     21