python numpy set elements of list by condition

Question

I want to set a specific element of my list to specific value with low overhead.
for example if I have this : a = numpy.array([1,2,3,0,4,0]) I want to change every 0 value to 10; in the end I want to have [1, 2, 3, 10, 4, 10]

in Matlab you can do this easily like a(a==0) = 10, is there any equivalent in numpy?

Asked By: Am1rr3zA

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Answer 1

Remarkably similar to Matlab:

>>> a[a == 0] = 10
>>> a
array([ 1,  2,  3, 10,  4, 10])

There’s a really nice "NumPy for Matlab Users" guide at the SciPy website.

I should note, this doesn’t work on regular Python lists. NumPy arrays are a different datatype that work a lot more like a Matlab matrix than a Python list in terms of access and math operators.

Answered By: mtrw

Answer 2

A little more pythonic way would be like this, I guess:

import numpy

a = numpy.array([1,2,3,0,4,0])
for k,v in enumerate(a):
    if v == 0:
        a[k] = 10
print a

Even more pythonic way (provided by @mtrw)

[10 if k == 0 else k for k in a]

Answered By: user1786283

python numpy set elements of list by condition

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