Delete array from array

Question

I want to delete elements from array A that may be found in array B.

For example:

A = numpy.array([1, 5, 17, 28, 5])
B = numpy.array([3, 5])
C = numpy.delete(A, B)

C= [1, 17, 28]

@Prune: Please don't dupe-close a NumPy-tagged question with a list question as the dupe target. — user2357112
– user2357112, Commented Aug 29, 2018 at 17:07

Maxime B · Accepted Answer · 2018-08-29 17:03:59Z

14

Numpy has a function for that :

numpy.setdiff1d(A, B)

That will give you a new array with the result you expect.

5 Comments

Antonis Over a year ago

Is numpy the fastest solution?

Maxime B Over a year ago

Sure is, numpy has C code running for most of its features.

Antonis Over a year ago

Thanks Maxime. System does not let be accept an answer yet. Got to wait 5 minutes.

user2357112 Over a year ago

Note that setdiff1d will sort the result and remove duplicates. If you don't want that, A[~numpy.isin(A, B)] will avoid the sort and deduplication, as long as A is actually an array and not the list you put in the question.

hpaulj Over a year ago

While a lot of numpy code is compiled, that's not true for all. You need to check the source to be sure. In this case setdiff1d uses np.unique and np.in1d which turn have Python code. It's heavily dependent on sorting.

Sruthi · Accepted Answer · 2018-08-29 17:16:15Z

7

You can try :

list(set(A)-set(B))
#[1, 28, 17]

Or a list comprehension :

[a for a in A if a not in B]

Another solution :

import numpy 
A[~numpy.isin(A, B)]
#array([ 1, 17, 28])

edited Aug 29, 2018 at 17:16

answered Aug 29, 2018 at 17:01

Sruthi

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1 Comment

Ray Toal Over a year ago

Might want to point out the set-based solution does not necessarily preserve the order of the elements in A.

Austin · Accepted Answer · 2018-08-29 17:02:49Z

4

Use a list-comprehension that iterates through A taking values that are not in B:

A = [1, 5, 17, 28, 5]
B = [3, 5]

print([x for x in A if x not in B])
# [1, 17, 28]

answered Aug 29, 2018 at 17:02

Austin

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Comments

whackamadoodle3000 · Accepted Answer · 2018-08-29 17:05:45Z

1

Try this

numpy.array([e for e in A if not e in B])

answered Aug 29, 2018 at 17:05

whackamadoodle3000

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2 Comments

Arpit Solanki Over a year ago

that's just copy of previous answers and adds no value

whackamadoodle3000 Over a year ago

Sorry, the other answers didn't load on my phone.

user10273157 · Accepted Answer · 2018-09-03 09:25:30Z

1

You can also try :

V= [7,12,8,22,1]
N= [12,22,0,1,80,82,83,100,200,1000]
def test(array1, array2):
    A = array1
    B = array2
    c = []
    for a in range(len(A)):
        boolian=False
        for b in range(len(B)):
            if A[a]==B[b]:
                boolian=True
        if boolian==False:
            c.append(A[a])
    print(c)


test(V,N)

answered Sep 3, 2018 at 9:25

user10273157

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