numpy.array operation / method: subtract value of one element from the value of next element

Question

I tried to build the differences from the values of one element [n] to the next element [n+1] in the same numpy.array.

This must be repeated for all n, I expect n-1 result values.
Furthermore I want to avoid using loops, because loops may be a source of errors numbering the elements.

Now I'm looking for an operation like:

result = array[n+1] - array[n]

for all n.

I tried much similar implementations, but I always get some error messages.

How can I make it work?

Welcome to stack overflow, you might want to take a look at how to format code so that it is readable and copy-pastable. Here are the guidelines to ask a good question. As for the answer itself, np.diff(array) does what you ask — gionni
– gionni, Commented Jul 6, 2017 at 16:27
np.diff() is what I looked for. Sometimes it is very easy with one keyword from an expert. Thank you gionni! — newbieTheNewest
– newbieTheNewest, Commented Jul 6, 2017 at 16:31
You are welcome pal, it can be hard to find what you are looking for in the beginning ;-) — gionni
– gionni, Commented Jul 6, 2017 at 16:37

gionni · Accepted Answer · 2017-07-06 20:43:37Z

3

Numpy's diff() function does what you ask.

Here is an example:

import numpy as np
a = np.arange(10)  # this instantiates a numpy array containing values from 0 to 9
result = np.diff(a)  # if you print this you'll see an array of 1 with length 9

If you want you can use slicing instead (I add this for all newbies, as an example of slicing), as follows:

result = a[1:] - a[:-1]

answered Jul 6, 2017 at 20:43

gionni

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cs95 · Accepted Answer · 2017-07-17 19:19:08Z

2

x = np.array([2,3,1,0])
result = x[:-1] - x[1:]

Output:

[-1,  2,  1]

edited Jul 17, 2017 at 19:19

cs95

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answered Jul 6, 2017 at 16:51

Rohan Ds

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