compare 2 array and return the index of the same value

Question

If I have a large array and a small array, for example

A = np.array([1,2,3])
B = np.array([3,4,5,6,7,8,2,1])

I can use np.intersect1d to get the same value, but if I want to get the index (in large array B)of same value, for this example,it should be [0,6,7],is there any command to get it?

Kasravnd · Accepted Answer · 2018-09-18 06:33:13Z

1

You can use np.in1d() to get a Boolean array that represents the places where items of A appears in B, then using np.where() or np.argwhere() function you can get the indices of the True items:

In [8]: np.where(np.in1d(B, A))[0]
Out[8]: array([0, 6, 7])

Or as mentioned in comments np.in1d(B, A).nonzero()[0]. However the way you wanna choose here depends pretty much on the reset of your program and where/how you wanna use the results. In addition you can run benchmarks on all the methods in both short and large arrays to see which one is more appropriate in which situation.

edited Sep 18, 2018 at 6:33

answered Sep 18, 2018 at 6:28

Kasravnd

108k19 gold badges167 silver badges195 bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

cs95 Over a year ago

Or maybe np.in1d(B, A).nonzero()[0]

Kasravnd Over a year ago

@coldspeed Sure, added to the answer.

Collectives™ on Stack Overflow

compare 2 array and return the index of the same value

1 Answer 1

2 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

2 Comments

Your Answer

Sign up or log in

Post as a guest

Related