Python dataframe sum rows

Question

If I have a dataframe with n rows, is there a way to set the ith row to be sum of row[i] and row[i-1] and do this so that the assignment to earlier rows is reflected in the latter rows? I would really like to avoid loops if possible.

Example DF:

             SPY   AAPL   GOOG
2011-01-10  0.44  -0.81   1.80
2011-01-11  0.00   0.00   0.00
2011-01-12 -1.11  -2.77  -0.86
2011-01-13 -0.91  -4.02  -0.68

Sample pseudo code of summing two rows:

DF[2011-01-11] = DF[2011-01-10] + DF[2011-01-11]
DF[2011-01-12] = DF[2011-01-11] + DF[2011-01-12]

and so on.

I think you mean to sum along columns. I suggest you change that (in the title if possible) to make this easier to find for over users — Mohammad Athar
– Mohammad Athar, Commented Oct 16, 2016 at 16:00

Steven G · Accepted Answer · 2016-10-16 15:41:37Z

1

based on your question, you are looking for a cumulative sum of each columns. you could use the cumsum() method

DF.cumsum()

               SPY    AAPL   GOOG
2011-01-10  0.4400 -0.8100 1.8000
2011-01-11  0.4400 -0.8100 1.8000
2011-01-12 -0.6700 -3.5800 0.9400
2011-01-13 -1.5800 -7.6000 0.2600

edited Oct 16, 2016 at 15:41

answered Oct 15, 2016 at 19:23

Steven G

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2 Comments

1nsg Over a year ago

No I did actually mean to say that.

1nsg Over a year ago

i. e. row[i]=row[i-1]+row[i] but row[i-1] is not the original row but rather the sum of row[i-1] and row[i-2]

piRSquared · Accepted Answer · 2016-10-15 19:25:09Z

0

Use DF.shift()

DF + DF.shift()

answered Oct 15, 2016 at 19:25

piRSquared

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