CODEWITHSUNDEEP
pythonnumpy
COMPCHEM
COMPCHEM

Reputation: 55

Converting 1D numpy array into top triangle of matrix

Is it possible to take a 1D numpy array containing 171 values and place these values into the top triangle of an 18X18 matrix?

I feel like I should be able to use np.triu_indices to do this somehow but I can't quite figure it out!

Thanks!

Upvotes: 5

Views: 1555

Answers (1)

hpaulj
hpaulj

Reputation: 231385

See What is the most efficient way to get this kind of matrix from a 1D numpy array? and Copy flat list of upper triangle entries to full matrix?

Roughly the approach is

result = np.zeros(...)
ind = np.triu_indices(...)
result[ind] = values

Details depend on the size of the target array, and the layout of your values in the target.

In [680]: ind = np.triu_indices(4)
In [681]: values = np.arange(16).reshape(4,4)[ind]
In [682]: result = np.zeros((4,4),int)
In [683]: result[ind]=values
In [684]: values
Out[684]: array([ 0,  1,  2,  3,  5,  6,  7, 10, 11, 15])
In [685]: result
Out[685]: 
array([[ 0,  1,  2,  3],
       [ 0,  5,  6,  7],
       [ 0,  0, 10, 11],
       [ 0,  0,  0, 15]])

Upvotes: 5

Related Questions