CODEWITHSUNDEEP
pythonnumpy
user3397243
user3397243

Reputation: 567

Comparing two numpy arrays and removing elements

I have been going through several solutions, but I am not able to find a solution I need.

I have two numpy arrays. Let's take a small example here. 

x = [1,2,3,4,5,6,7,8,9]
y = [3,4,5]

I want to compare x and y, and remove those values of x that are in y.

So I expect my final_x to be 

final_x = [1,2,6,7,8,9]

I found out that np.in1d returns a boolean array the same length as x that is True where an element of x is in y and False otherwise. But how do I use it, if not any other method to get my final_x.??

Upvotes: 2

Views: 2950

Answers (3)

Lord Henry Wotton
Lord Henry Wotton

Reputation: 1362

You can use built-in sets:

final_x = set(x) - set(y)

and subtract the second from the first. You can convert final_x to a list or numpy.array if you feel so inclined.

Upvotes: 0

Ffisegydd
Ffisegydd

Reputation: 53678

If you really do have numpy arrays then you can use numpy.setdiff1d as below

import numpy as np

x = np.array([1,2,3,4,5,6,7,8,9])
y = np.array([3,4,5])

z = np.setdiff1d(x, y)
# array([1, 2, 6, 7, 8, 9])

Upvotes: 6

Ashwini Chaudhary
Ashwini Chaudhary

Reputation: 250891

Simply pass the negated version of boolean array returned by np.in1d to array x:

>>> x = np.array([1,2,3,4,5,6,7,8,9])
>>> y = [3,4,5]
>>> x[~np.in1d(x, y)]
array([1, 2, 6, 7, 8, 9])

Upvotes: 3

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