CODEWITHSUNDEEP
pythonarraysnumpyindexingboolean
morepenguins
morepenguins

Reputation: 1277

How to Use Boolean Array to Replace Specific Indices in Python

I have a numpy and a boolean array:

nparray = [ 12.66  12.75  12.01  13.51  13.67 ]
bool = [ True False False True True ]

I would like to replace all the values in nparray by the same value divided by 3 where bool is False.

I am a student, and I'm reasonably new to python indexing. Any advice or suggestions are greatly appreciated!

Upvotes: 1

Views: 3956

Answers (3)

diegueus9
diegueus9

Reputation: 31532

With just python you can do it like this:

nparray = [12.66, 12.75, 12.01, 13.51, 13.67]
bool = [True, False, False, True, True]
map(lambda x, y: x if y else x/3.0, nparray, bool)

And the result is:

[12.66, 4.25, 4.003333333333333, 13.51, 13.67]

Upvotes: 0

Grr
Grr

Reputation: 16079

naming an array bool might not be the best idea. As ayhan did try renaming it to bl or something else.

You can use numpy.where see the docs here

nparray2 = np.where(bl == False, nparray/3, nparray)

Upvotes: 2

user2285236
user2285236

Reputation:

Use boolean indexing with ~ as the negation operator:

arr = np.array([12.66, 12.75, 12.01, 13.51, 13.67 ])
bl = np.array([True, False, False, True ,True])

arr[~bl] = arr[~bl] / 3
array([ 12.66      ,   4.25      ,   4.00333333,  13.51      ,  13.67      ])

Upvotes: 1

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