Casting a vector into a matrix in Python using for-loops

Question

I have a list of length 50 created using linspace:

m=np.linspace(0,10,50)

I can recast this as a 10 X 5 matrix using reshape

X=np.reshape(m,(10,5))

But, if I want to use for-loops to do the same thing, I get an error:

z=np.zeros((10,5),dtype=float)
s=0
for i in range(0,10):
    for j in range(0,5):
        m[i][j]=z[s]
        s=s+1

here is the error:

'numpy.float64' object does not support item assignment

Why isn't the item assignment supported?

Thanks

What is the variable m? Your code assumes that it's already some 2D structure, but you've never defined it. — Prune
– Prune, Commented Apr 1, 2020 at 21:42

kederrac · Accepted Answer · 2020-04-01 21:42:25Z

1

z will store your items from m after the reshape :

m=np.linspace(0,10,50)

z=np.zeros((10,5),dtype=float)
for i in range(10):
    for j in range(5):
        z[i][j]=m[i * 5 + j]  # compute the index from m base on the current row and column


print(z)

answered Apr 1, 2020 at 21:42

kederrac

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Comments

Navid Asgari · Accepted Answer · 2020-04-01 21:54:12Z

0

It was a silly mistake:

yes, I got the sizes wrong; this is how I rewrote it:

m=np.linspace(0,10,50)
z=np.zeros((10,5),dtype=float)
s=0
for i in range(0,10):
    for j in range(0,5):
        z[i][j]=m[s]
        s=s+1

answered Apr 1, 2020 at 21:54

Navid Asgari

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