CODEWITHSUNDEEP
pythonarraysnumpy
Will.S89
Will.S89

Reputation: 327

Merge two numpy arrays and delete duplicates?

I have one numpy array =

[1,6,7,9,3,5]

and a second numpy array =

[3,5,8,9,2]

I would like to merge these two arrays together:

[1,6,7,9,3,5,3,5,8,9,2]

and then remove the duplicates in the numpy array to get :

[1,6,7,9,3,5,8,2]

I would like to keep as much of array one as possible and take out elements of array two, that don't appear in array one, and append these.

I am not sure if it makes more sense to:

  1. merge both arrays and remove duplicates. or
  2. loop through elements of array 2, and if they don't appear in array 1 then concatenate to array 1.

I have tried using various loops but these appear to work mostly for lists, I have also tried using set() but this orders the numpy array, I would like to keep the random order form.

Upvotes: 3

Views: 8506

Answers (2)

Gerges
Gerges

Reputation: 6509

Here is slightly different way to do it also: 

z = np.concatenate([x, y[~np.isin(y,x)])

Upvotes: 4

user3483203
user3483203

Reputation: 51155

To join the two arrays, you can simply use np.concatenate

Removing duplicates while preserving order is a bit tricky, because normally np.unique also sorts, but you can use return_index then sort to get around this:

In [61]: x
Out[61]: array([1, 6, 7, 9, 3, 5])

In [62]: y
Out[62]: array([3, 5, 8, 9, 2])

In [63]: z = np.concatenate((x, y))

In [64]: z
Out[64]: array([1, 6, 7, 9, 3, 5, 3, 5, 8, 9, 2])

In [65]: _, i = np.unique(z, return_index=True)

In [66]: z[np.sort(i)]
Out[66]: array([1, 6, 7, 9, 3, 5, 8, 2])

Upvotes: 11

Related Questions