How check if pair of values exist in 2d Matlab array?

Question

Say I have

a=[1 2 3 4; 5 6 7 8];

If I then have x=3, y=7, how can I check that (3,7) exists in array a but also ensure that if I check for the pair x=3, y=8 (3,8), then it returns false and NOT true?

EDIT: (3,7) should return true but (3,8) false because 3 and 7 are in the same column, but 3 and 8 are not. Also (7,3) should be false because for (x,y), xcorresponds to element in 1st row and y in 2nd row

EDIT2: I see isPresent = any(ismember(a.', [x y], 'rows')); for the arrray a.

But what if I have this: b=[1 5; 2 6; 3 7; 4 8]. Then how can I ensure that (3,7) is true but (7,3) is false?

Why would (3,8) return false, because (3,7) was already found, because 3 and 8 are not in the same column, or something else? — beaker
– beaker, Commented May 23, 2018 at 22:19
@user5739619 In the second example, 3 does not exist in the first row, nor does 7 exist in the second row. Please be explicit about the dimensions in which you are searching. — beaker
– beaker, Commented May 23, 2018 at 22:47

beaker · Accepted Answer · 2018-05-23 22:26:19Z

4

The easiest way is to use ismember, but it works on rows instead of columns, so we'll need to transpose the matrix first:

x = 3;
y = 7;
a=[1 2 3 4; 5 6 7 8];

isPresent = any(ismember(a.', [x y], 'rows'));

>> isPresent
isPresent = 1

answered May 23, 2018 at 22:26

beaker

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2 Comments

user5739619 Over a year ago

Yes, that works. But what if I have this: b=[1 5; 2 6; 3 7; 4 8]. Then how can I ensure that (3,7) is true but (7,3) is false?

Sardar Usama Over a year ago

don't transpose then

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