Finding the summation of values from two pandas dataframe column

Question

I have a pandas dataframe like below

import pandas as pd
data = [[5, 10], [4, 20], [15, 30], [20, 15], [12, 14], [5, 5]]
df = pd.DataFrame(data, columns=['x', 'y'])

I am trying to attain the value of this expression.

I havnt got an idea how to mutiply first value in a column with 2nd value in another column like in the expression.

Asked By: imhans4305

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Source

Answer 1

You can use pandas.DataFrame.shift(). You can one times compute shift(-1) and use it for 'x' and 'y'.

>>> df_tmp = df.shift(-1)
>>> (df['x']*df_tmp['y'] - df_tmp['x']*df['y']).sum() * 0.5
-202.5

# Explanation
>>> df[['x+1', 'y+1']] = df.shift(-1)
>>> df
    x   y   x+1   y+1
0   5  10   4.0  20.0 # x*(y+1) - y*(x+1) = 5*20 - 10*4
1   4  20  15.0  30.0
2  15  30  20.0  15.0
3  20  15  12.0  14.0
4  12  14   5.0   5.0
5   5   5   NaN   NaN

Answered By: I'mahdi

Answer 2

Try pd.DataFrame.shift() but I think you need to enter -1 into shift judging by the summation notation you posted. i + 1 implies using the next x or y, so shift needs to use a negative integer to shift 1 number ahead. Positive integers in shift go backwards.

Can you confirm 320 is the right answer?

0.5 * ((df.x * df.y.shift(-1)) - (df.x.shift(-1) + df.y)).sum()

>>>320

Answered By: user16367225

Answer 3

I think the below code has the correct value in expresion_end

import pandas as pd
data = [[5, 10], [4, 20], [15, 30], [20, 15], [12, 14], [5, 5]]
df = pd.DataFrame(data, columns=['x', 'y'])

df["x+1"]=df["x"].shift(periods=-1)
df["y+1"]=df["y"].shift(periods=-1)
df["exp"]=df["x"]*df["y+1"]-df["x+1"]*df["y"]
expresion_end=0.5*df["exp"].sum()

Answered By: Atanas Atanasov

Finding the summation of values from two pandas dataframe column

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