I have a column subtraction how can i do it in python-CodePudding

i Have a cross subtraction problem and i will like to have the solution for the same i have a data frame as shown below

input Y = 2

|X  | A | Z  |
|20 | 0 |18  |
|30 | 0 |-12 |
|40 | 0 |-52 |
|50 | 0 |-102|
    :
    :
    :

The formulae for this is Y is given as a input by the user, where

z(row1) = x(row1) - Y
z(row2) = z(row1) - x(row2)
z(row3) = z(row2) - x(row3)
:
:
so on......

is there a way to code this using python using loops?

CodePudding user response：

You are effectively doing a cumulative sum with negative values and an offset of y (except for the first row)

y = 2    
df.loc[:, 'Z'] = -df['X'].cumsum()   [40]*df.index.size - [y]*df.index.size

The addition of 40 is to undo the negation in the first row, or in other words

df.loc[:, 'Z'] = -df['X'].cumsum()   [2*df.loc[0]['X']]*df.index.size - [y]*df.index.size

print(df)
#    X    Z
#0  20   18
#1  30  -12
#2  40  -52
#3  50 -102

CodePudding user response：

Since you're only working with the input once I would not put the first equation into the loop. If you want to store the data of x you have to add this as well

x = 20    
z[0] = x - y
for i in range(9): # where 9 is number of rows you want to add
    x  = 10
    z[i 1] = z[i] - x