Numpy reshape "reversal"

Question

I read a 4D array from a file which is given in a 2D form i, j, k, x, y, z. Input file header and shape I use numpy.reshape to reshape the 2D array to it's 3-D form. After making changes to this, I wish to write the file exactly the same order / format as I read it. I do not understand how to "reverse" numpy.reshape to put it back in the same format.

import numpy as np    
import pandas as pd
from pandas import read_csv 


header = read_csv("Input/Grid1_test.csv", nrows=1,skipinitialspace=True)

print header.head()

imax=header['IMAX'].iloc[0]
jmax=header['JMAX'].iloc[0]
kmax=header['KMAX '].iloc[0]

print(imax,jmax,kmax)

#read grid data with numpy array .. it is slow but probably worth it 
grid_data = np.loadtxt('Input/Grid1_test.csv', delimiter=',', skiprows=3)


size_arr = np.array(grid_data).reshape(kmax, jmax, imax, 6)

#do something

#write the grid back into the file

Henry · Accepted Answer · 2019-08-22 21:54:25Z

7

To "reverse" a reshape, you can just call reshape again on the array to reshape it into the original dimensions.

If you have an array x with dimensions (n, m) then:

x.reshape(kmax, jmax, imax, 6).reshape(n, m) == x

edited Aug 22, 2019 at 21:54

answered Aug 2, 2018 at 0:00

Henry

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1 Comment

Baron Over a year ago

Thanks Henry, that works! I should have thought of it :)

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