Writing numpy array in a text file-CodePudding

I have encountered an error while trying to write a numpy error into a text file. To put the question the below code

import numpy as np

a = np.arange(1,10)
sigma = open("sample",'w')
for row in a:
    np.savetxt(sigma,row)
sigma.close()

gives an error ValueError: Expected 1D or 2D array, got 0D array instead

I worked around it with this code:

a = np.arange(1,10)
sigma = open("sample",'w')
np.savetxt(sigma,a, newline="\n")
sigma.close()

But I still do not now why my first attempt didn't work. Why my array appears 0D? (I'm using python 3.9.9)

CodePudding user response：

As is mentioned in the comments, the for loop is your problem, this is because when you iterate over a one dimensional array you get scalars:

import numpy as np

a = np.arange(1,10)
sigma = open("sample",'w')
np.savetxt(sigma,a)
sigma.close()

Result:

1.000000000000000000e 00
2.000000000000000000e 00
3.000000000000000000e 00
4.000000000000000000e 00
5.000000000000000000e 00
6.000000000000000000e 00
7.000000000000000000e 00
8.000000000000000000e 00
9.000000000000000000e 00

CodePudding user response：

The first attempt does not work because a is a one-dimensional array, so "row" loops over each element of a, meaning "row" is a 0D array. Since np.savetxt() only works for one or two dimensional array, it fails.