numpy iterating over multidimensional array

Question

I am very new to numpy and I am trying to achieve the following in the most pythonic way. So, I have two arrays:

a=array([[0, 1, 2],[3,4,5]])
b=zeros(a.shape)

Now, what I would like is for each element in b for be one greater than the value of the corresponding element in a i.e b=a+1

I was wondering how this can be achieved in numpy.

Ionut Hulub · Accepted Answer · 2013-03-09 22:28:53Z

3

The easiest way is the following:

b = a + 1

But if you want to iterate over the array yourself (although not recommended):

for i in range(len(a)):
    for j in range(len(a[i])):
        b[i][j] = a[i][j] + 1

edited Mar 9, 2013 at 22:28

answered Mar 9, 2013 at 22:21

Ionut Hulub

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12 Comments

user2152572 Over a year ago

I want 1 added to each element of a, and thus form b - if that makes sense..The answer iam looking is b=[[1,2,3],[4,5,6]]

user2152572 Over a year ago

Ionut: Sorry, but I was looking to learn how to iterate over multidimensional arrays - although your solution does work for this situation..

user2152572 Over a year ago

Ionut: Thanks a lot for this! really appreciate this help. I have been trying to look around, but not much luck.

Benjamin Hodgson Over a year ago

@user2152572 b = a + 1 is the right answer. You don't ever want to iterate over an ndarray because it'll be too slow. Numpy is designed for 'vectorized' calculations: if you use Numpy routines (rather than looping) you'll get the result much quicker.

Ionut Hulub Over a year ago

What poorsod was saying is that using the numpy routines is a lot faster then iterating through the array yourself, but you may do so if it's for learning purposes.

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