How to fill an array in python with given list of values and list of indices?

Question

What would be the simplest (fastest) way to take as input the following :

M=np.zeros((2,5))  
values=[a,b,c] #a,b and c are integers  
indices=[(1,2,4),(0,2,4)]

and have as an output :

M=[[0,a,b,0,c],[a,0,b,0,c]]

So in your indices, the numbers in the tuples represent where the values go? (example: (0,2,4) -> [a, 0 , b, 0 ,c] correct?) — jasonmzx
– jasonmzx, Commented Feb 23, 2021 at 15:38
What do you mean by "simplest"? Shortest code? Most idiomatic? Least brainpower used to come up with a solution? — Reti43
– Reti43, Commented Feb 23, 2021 at 15:41

Epsi95 · Accepted Answer · 2021-02-23 15:57:04Z

2

try indexing

M = np.zeros((2,5))
values = [7,8,9]   
indices = np.array([[1,2,4],[0,2,4]])

M[np.arange(M.shape[0])[:,None],indices] = values

print(M)

[[0. 7. 8. 0. 9.]
 [7. 0. 8. 0. 9.]]

answered Feb 23, 2021 at 15:52

Epsi95

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