How to populate an 2D array from a list left to right with the diagonal being all zeroes

Question:

I have a list:

idmatrixlist=[0.61, 0.63, 0.54, 0.82, 0.58, 0.57]

I need to populate an array from left to right while maintaining the zeroes on the diagonal so that the resulting array looks like.

enter image description here

I have tried the following code but it results in the wrong ordering of the entries.

lowertriangleidmatrix = np.zeros((4,4))
indexer = np.tril_indices(4,k=-1)
lowertriangleidmatrix[indexer] = idmatrixlist
print(lowertriangleidmatrix)

result:
[[0.   0.   0.   0.  ]
 [0.61 0.   0.   0.  ]
 [0.63 0.54 0.   0.  ]
 [0.82 0.58 0.57 0.  ]]

How can this be re-ordered?

Asked By: Jamie

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Source

Answers:

You can use triu_indices and invert the x/y:

lowertriangleidmatrix = np.zeros((4, 4))

indexer = np.triu_indices(4, k=1)[::-1]
# (array([0, 0, 1, 0, 1, 2]), array([1, 2, 2, 3, 3, 3]))

lowertriangleidmatrix[indexer] = idmatrixlist

print(lowertriangleidmatrix)

Output:

[[0.   0.   0.   0.  ]
 [0.61 0.   0.   0.  ]
 [0.63 0.82 0.   0.  ]
 [0.54 0.58 0.57 0.  ]]
Answered By: mozway