how to store and read 4d numpy array

Question

I am new to Python. I am trying to store a 4d numpy array in a file (done it) and read the values of this file (there's the problem). The code is:

import numpy as np

Lx=6;Ly=6,Lz=2 
mat=np.zeros((Lx,Ly,Lz,3),dtype=np.float)

mat=np.random.rand(Lx,Ly,Lz,3)

outfile=open("config.txt","w")


for i in range(0,Lx):
    for j in range(0,Ly):
        for k in range(0,Lz):
           print(mat[i,j,k,0], mat[i,j,k,1], mat[i,j,k,2],file=outfile)

outfile.close() 


mnew=np.zeros((Lx,Ly,Lz,3),dtype=np.float)

infile=open("config.txt","r")

for i in range(0,Lx):
    for j in range(0,Ly):
        for k in range(0,Lz):
            infile.read(mnew[i,j,k,0], mnew[i,j,k,1], mnew[i,j,k,2])

I get the error:

infile.read(mnew[i,j,k,0], mnew[i,j,k,1], mnew[i,j,k,2]) TypeError: read() takes at most 1 argument (3 given)

but I don't know how to fix it

Thanks, M

Python's read function of files reads from files, but it does not read directly into variables. If you insist on using read like such without using proper numpy functions for loading and saving files, what I think you want is to read the lines using readlines and insert into variables — Zionsof
– Zionsof, Commented May 16, 2019 at 11:06

Koen G. · Accepted Answer · 2019-05-16 15:45:40Z

1

The easiest solution to save and read numpy arrays is to just use numpy functions np.save and np.load.

import numpy as np
example = np.random.rand(6, 6, 2, 3)

#save
example.save('example.npy')

#read back
example_copy = np.load('example.npy')

edited May 16, 2019 at 15:45

answered May 16, 2019 at 10:44

Koen G.

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4 Comments

geom Over a year ago

this is a 4d matrix, not an array

Daniel F Over a year ago

@mgeo in numpy terms array means ndarray, which can have arbitrary dimension. mat and mnew are already ndarrays

geom Over a year ago

thanks, I tried: with open('newstore','w') as ff: np.save(ff,mat) ff.closed mnew=np.load(ff) but it didn't work

Koen G. Over a year ago

You can even skip the open with these functions. I added a minimal example.

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