sum column above/below current row in pandas

Question

I'm trying to achieve this in pandas:

df['X'] = df['C'].where(row is <= current row).sum()
df['Y'] = df['C'].where(row is >= current row).sum()

What is the right syntax to make pandas sum the data from column C that are above or equal to the current row?

Quang Hoang · Accepted Answer · 2020-10-08 14:41:34Z

6

This is cumsum:

df['X'] = df['C'].cumsum()
df['Y'] = df['C'].sum() + df['C'] - df['X']
# or 
# df['Y'] = df.iloc[::-1].cumsum()

answered Oct 8, 2020 at 14:41

Quang Hoang

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3 Comments

very needed question and answer

follow up question: if I need to exclude the current row itself (aka, "row <" vs "row <="), is there an easy way to make cumsum do that?

@Brannon cumsum won't do, but combined with shift does: df['C'].shift().cumsum().

BENY · Accepted Answer · 2020-10-08 15:25:36Z

2

Let us try with expanding you can chose the agg function you need etc, mean/std

df['X'] = df['C'].expanding().sum()
df['Y'] = df['C'].iloc[::-1].expanding().sum()

answered Oct 8, 2020 at 14:44

BENY

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