Adding new lines results in ValueError in numpy.asarray

Question

Prior to adding the neighbor statements (that I commented with 'new'), everything worked just fine. Now, when using numpy.asarray, there is following error:

ValueError: could not broadcast input array from shape (3,3) into shape (3).

I'm really confused as the new lines didn't change anything about the rotations-array.

def rre(mesh, rotations):
"""
Relative Rotation Encoding (RRE).
Return a compact representation of all relative face rotations.
"""
all_rel_rotations = neighbors = []
for f in mesh.faces():
    temp = [] # new
    for n in mesh.ff(f):
        rel_rotation = np.matmul(rotations[f.idx()], np.linalg.inv(rotations[n.idx()]))
        all_rel_rotations.append(rel_rotation)
        temp.append(n.idx()) # new
    neighbors.append(temp) # new
all_rel_rotations = np.asarray(all_rel_rotations)
neighbors = np.asarray(neighbors) # new
return all_rel_rotations, neighbors

could you please edit the code to also provide an example of input and output? — Francesco Montesano, May 04 '19 at 17:15
Print the value of `neighbors` before `neighbors = np.asarray(neighbors)`. — unutbu, May 04 '19 at 17:16
Possible duplicate: [ValueError: could not broadcast input array from shape (224,224,3) into shape (224,224)](https://stackoverflow.com/q/43977463/190597). — unutbu, May 04 '19 at 17:17

Francesco Montesano · Accepted Answer · 2019-05-04T17:25:02.580

2

The source of the problem is very likely the line:

all_rel_rotations = neighbors = []

In Python lists are mutables and all_rel_rotations and neighbors point to the same list, so if you do all_rel_rotations.append(42) you will see that neighbors = [42, ]

The line:

all_rel_rotations.append(rel_rotation)

appends a 2D array, while

neighbors.append(temp)

appends a 1D array (or the other way around) to the same list. Then:

all_rel_rotations = np.asarray(all_rel_rotations)

tries to convert to an array and get confused.

If you need to list do

all_rel_rotations = []
neighbors = []

edited May 04 '19 at 17:25

answered May 04 '19 at 17:21

Francesco Montesano

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This is an error that everyone starting with python does: one must learn the difference between mutables and non-mutables variables and how they are handled it the hard way :D. – Francesco Montesano May 04 '19 at 17:28
Well, at least this particular one will never happen again. You probably saved me hours of searching and frustration :) – Rani May 04 '19 at 17:31
To save you hours in the future I suggest to learn to use the python debugger as soon as possible – Francesco Montesano May 04 '19 at 18:30

Adding new lines results in ValueError in numpy.asarray

1 Answers1