How to update an array in Python based on another array?

Question

I have two arrays in Python.

array1 looks like this:

[[ 59.13425446  85.62345123]
 [ 59.4981575   87.67746735]
 [ 57.4234575   83.34333335]]

array2 looks like this:

[[ 255  255]
 [ 1.0   255]
 [ 255   1.0]]

I want to update array1. For every value in array2 that equals 1.0, I want to update array1 with a value of 0.0. In the end it should look like this:

[[ 59.13425446  85.62345123]
 [ 0.0   87.67746735]
 [ 57.4234575   0.0]]

How can I do this in Python?

Lev Levitsky · Accepted Answer · 2013-11-15 19:58:58Z

5

Something like:

array1[array2 == 1] = 0

answered Nov 15, 2013 at 19:58

Lev Levitsky

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3 Comments

Jas Over a year ago

This looks muuuuch cleaner than mine but didnt seem to work. The output was [0, [59.4981575, 87.67746735], [57.4234575, 83.34333335]]. Did you get something else?

Nick T Over a year ago

@Jas are you using (numpy) arrays or lists?

Lev Levitsky Over a year ago

@Jas This method doesn't work for regular Python lists. array2 == 1 returns just False if array2 is a list. With numpy arrays, the expression evaluates to an array of bools, which are then used as indexes for the assignment.

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