Using a ''for loop'' to copy numpy arrays

Question

I have 2 numpy arrays:

array1 = np.load(r'C:\Users\x\array1.npy')
array2 = np.load(r'C:\Users\x\array2.npy')

I have to merge them in single array, so what I did was:

merg_arr = np.zeros((len(array1)+len(array2), 4, 100, 100), dtype=input_img.dtype)

for i in range(len(array1)+len(array2)):
    if i < len(array1):
        merg_arr[i] = array1[i]
    else:
        merge_arr[i] = array2[i-len(array1)]

It works in that way in case of 2 input arrays. Now I have 5 input arrays instead of two. But I am confused how to use the for loop in this case?

The shape of the 5 arrays and the expected output are:

array1: (7, 4 ,100, 100) 
array2: (14, 4 ,100, 100) 
array3: (5, 4 ,100, 100) 
array4: (8, 4 ,100, 100) 
array5: (66, 4 ,100, 100)
merg_arr: (100,4,100,100)

See how to create a Minimal, Complete, and Verifiable example — keepAlive
– keepAlive, Commented May 8, 2017 at 15:31

MSeifert · Accepted Answer · 2017-05-08 16:22:54Z

3

You could simply concatenate them along the first axis:

merg_arr = np.concatenate([array1, array2, array3, array4, array5], axis=0)

You can also do it with the for-loop:

arrays = (array1, array2, array3, array4, array5)
length_sum = sum(len(arr) for arr in arrays)
merge_arr = np.zeros((length_sum, 4,100,100), dtype=arrays[0].dtype)
start = 0
for arr in arrays:
    end = start + len(arr)
    merge_arr[start:end] = arr
    start = end

However concatenate is probably much easier.

edited May 8, 2017 at 16:22

answered May 8, 2017 at 15:31

MSeifert

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