CODEWITHSUNDEEP
arraysmatlabrepeat
Jeremy McNees
Jeremy McNees

Reputation: 787

Remove Non-repeating Values from an Array

I have a large array in which certain row values repeat (8 repeats max). How can I only pull the repeated row values and their subsequent columns?

I should mention that the first column is an ID column (where I want to look for repeats), but the repeated ID values have different column values.

ID = [1;2;4;10;7;1;5;4]

I want to locate row n of both instances of 1, and 4

Output should be:

ID = [1;4;1;4]

or the sorted version:

ID=[1;1;4;4]

Either version is workable.

I believe I need a loop and the use of the find function

Upvotes: 1

Views: 566

Answers (2)

Notlikethat
Notlikethat

Reputation: 20914

The sorted approach is also simple:

ID = sort(ID);
index = find(ID(2:end) == ID(1:end-1));
ID = ID(index);

Upvotes: 2

Stewie Griffin
Stewie Griffin

Reputation: 14939

You can use histc, in combination with ismember, find and unique this way:

[n, bin] = histc(A, unique(A));
multiple = find(n > 1);
index = find(ismember(bin, multiple))
index =
     1
     3
     6
     8

Which gives:

ID(index)
     1
     4
     1
     4

Upvotes: 2

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