How to subtract values in a list

November 30, 2022

I am writing a function that works as follows it receives list of numbers e.g [0.5,-0.5,1]
then it returns a list with this in each index[(-0.5-0.5) + (1-0.5)]. In other words, it adds the difference between the current value and the other values. So the output should be [-0.5,2.5,-2]

def  Calculate(initial_values,b):
   x = np.array([initial_values]).T
   results=[0]
   for i in range(len(initial_values)):
     results.append( (initial_values[:i] - initial_values[i])+(initial_values[i+1:]-initial_values[i])

Error

TypeError: unsupported operand type(s) for -: 'list' and 'float'

>Solution :

This seems to do the trick:

def Calculate(arr):
    res = []
    for i, val in enumerate(arr):
        total = -val * (len(arr) - 1) + sum(arr[0:i]) + sum(arr[i+1:])
        res.append(total)
    return res

We iterate through each element and calculate the sum of differences like you described. Since the current element gets subtracted from each term we can factor it out.