append versus resize for numpy array

Question

I would like to append a value at the end of my numpy.array. I saw numpy.append function but this performs an exact copy of the original array adding at last my new value. I would like to avoid copies since my arrays are big.

I am using resize method and then set the last index available to the new value. Can you confirm that resize is the best way to append a value at the end? Is it not moving memory around someway?

oldSize = myArray,shape(0)
myArray.resize( oldSize + 1 )
myArray[oldSize] = newValue

This may be of use to you: stackoverflow.com/questions/2345518/numpy-array-memory-issue. But it may not :) — mtrw
– mtrw, Commented May 26, 2010 at 7:54

Community · Accepted Answer · 2017-05-23 11:45:36Z

8

My simple timing experiment of append vs. resizing showed that resizing is about 3x faster and its the fastest way that I can think of to do this. Also, the answer to this question seems to imply that resizing the array is the way to go because it is in-place.

Verdict: Use resize

P.S. You also might want to check out this discussion from a numpy mailing list.

edited May 23, 2017 at 11:45

CommunityBot

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answered May 25, 2010 at 21:46

Justin Peel

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