CODEWITHSUNDEEP
matlab
Christina
Christina

Reputation: 935

Test the equality of some elements and/or columns in matlab

I have two matrices:

$X$ =

 1     2     3
 4     5     6
 7     8     9

$Y$ =

 1    10    11
 4    12    13
 7    14    15

I know that if I want to find the index of a specific element in $X$ or $Y$, I can use the function ''find''. For example: $index_3 = find(X==3)$.

1) My first question is how can i find (or test) if $X$ contains some elements that are also present in $Y$? can I use the function ''find''? if yes so how?

2) The second question is related to the first. Now I want to find (or test) if some columns in $X$ are also present in $Y$. For example, how can I demonstrate in matlab that the column $[1;2;3]$ in $X$ is also present in $Y$?

Any help will be very appreciated.

Upvotes: 0

Views: 45

Answers (1)

beaker
beaker

Reputation: 16810

You can do both of these with ismember. For the first one, it's simply:

locsX = ismember(X, Y);

For your test matrices this gives you:

locsX =

   1   0   0
   1   0   0
   1   0   0

For another example:

X =

   1   2   3
   4   5   6
   7   8   9

Z =

    1    7   13
    3    9   15
    5   11   17

>> ismember(X, Z)
ans =

   1   0   1
   0   1   0
   1   0   1

For the second part of your question, ismember has an optional flag to compare rows:

rowsX = ismember(X, Y, 'rows');

so to get the columns, just take the transpose of both matrices:

rowsX = ismember(X.', Y.', 'rows')

rowsX =

   1
   0
   0

Upvotes: 1

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