Python combine 2 un nested for loops to get result-CodePudding

Why is my code below not working correctly? The answer for d3 is getting calculated incorrectly. I want d3 to be [-1,1,3] but instead I am getting [1,2,3]. How can I fix this code?

x = [1,2,3]
z = 3 
y = [4,5,6]
d =[]
for i in range(3):
    d1 = x[i]-z # [-2,-1,0]
for j in range(3):
    d2 = y[j]-z # [1,2,3]
    d3 = d1 d2 # [-1,1,3]
    d.append(d3)
for i in d :
    print (i)

CodePudding user response：

There doesn't seem to be a need for the second 'for' loop. This achieves what I think you are looking for:

x = [1,2,3]
z = 3 
y = [4,5,6]
d =[]
for i in range(3):
    d1 = x[i]-z # [-2,-1,0]
    d2 = y[i]-z # [1,2,3]
    d3 = d1 d2 # [-1,1,3]
    d.append(d3)
for i in d :
    print (i)

When you start a second 'for' loop to iterate indexes of 'y', you are only going to get the last index of 'for' loop iterating over 'x'.

CodePudding user response：

This can be done using one list comprehension:

x = [1,2,3]
z = 3 
y = [4,5,6]

d = [a   b - z*2 for a, b in zip(x, y)]

Or for a numpy approach (which is overboard but what the heck)

import numpy as np

x = np.array([1,2,3])
z = 3 
y = np.array([4,5,6])

d = x   y - z*2

CodePudding user response：

I couldn't understand the context, but if you want d3 to be [-1,1,3]. You need to place both d1 and d2 within the same loop.

x = [1,2,3]
z = 3 
y = [4,5,6]
d =[]
for i in range(3):
    d1 = x[i]-z # [-2,-1,0]
    d2 = y[i]-z # [1,2,3]
    d3 = d1 d2 # [-1,1,3]
    d.append(d3)
for i in d :
    print (i)

CodePudding user response：

Looking at what you have commented in your question as to what the lists look like, I think this is what you require:

x = [1,2,3]
z = 3 
y = [4,5,6]
d1 = [(e - z) for e in x]   # [-2,-1,0]
d2 = [(e - z) for e in y]   # [1,2,3]
d3 = [ a   b for a, b in zip(d1, d2)]  # [-1,1,3]

for i in d3:
    print(i)

Output:

-1
1
3

CodePudding user response：

You must iterate over a list and get the sum you want:

x = [1,2,3]
z = 3 
y = [4,5,6]
d =[]
d1 = []
d2 = []
for i in range(3):
    x1 = x[i]-z # [-2,-1,0]
    d1.append(x1)
for j in range(3):
    y1 = y[j]-z # [1,2,3]
    d2.append(y1)
    
for k in range(3):
    d3 = d1[k]   d2[k]
    d.append(d3)
for i in range(3):
    print(d[i])