Finding X value corresponds to a particular Y value?

I have a matrix , X=[5 6 9 8 4] Y=[8 7 2 1 9] If I plot this and I need to get position of the X value corresponds to Y=1, that means in which row the X value 8 is located? answer should be 4th position. How do I find this if the size of matrix is very big.. Please help me

[Pooja Patel]

value = find(Y == Y); xaty = x(value) or u can take find(Y == 1) this will also work if size is big

[Guillaume]

@Pooja Patel

value = find(Y == Y)

That is exactly the same as

value = 1:numel(Y)

Answer 1

[Andrei Bobrov]

X=[5 6 9 8 4];
Y=[8 7 2 1 9];

idx = find(Y == 1);
Xidx = X(idx);

[jop schilder]

and how does this work if i want to retrieve mulitple values at once? so if i want

idx = find (Y == 1&2&7)

[Thomas]

Thanks Andrei Bobrov level 9 MVP on 15 Jul 2013! I was able to finish my code for homework because of you!

[Image Analyst]

@jop schilder you would do that this way

mask = (Y == 1) | (Y == 2) | (Y == 7); % Logical vector (Only 0's and 1's)
indexes = find (mark) % Vector of actual index locations (e.g. [39, 123, 348, 983, 8943, ....etc.]