Finding column 2 values for column 1 value in a multidimensional array

I have a (:,2) array of data, where column 1 are x-values and column 2 are y-values.

I have a calculated y-value saved as a variable (like B shown below), and I want to:

(1) locate the y-values closest to my variable B and (2) extract the x-values that correspond to these y-values.

For the example below, I would want to find the y-values 0.11 and then extract the x-values 0.22 and 0.33 into an array.

Here is a simplified version of my issue:

A = [0.22 0.11; 0.33 0.11; 0.55 0.66]

A =

0.2200 0.1100

0.3300 0.1100

0.5500 0.6600

B = 0.12;

B1 = 0.12 + 0.01;

B2 = 0.12 - 0.01;

idx = find(A < B1 && A > B2);

I get this error: Operands to the || and && operators must be convertible to logical scalar values.

Can I not use variables when setting conditions for find? I am a MATLAB novice so any help would be much appreciated!

Answer 1

[madhan ravi]

A = [0.22 0.11; 0.33 0.11; 0.55 0.66];
B = 0.12;
idx=ismembertol(A,B,0.1);
x=A(any(idx,2),1)
y=A(any(idx,2),2)

Gives:

x =

    0.2200
    0.3300

y =

    0.1100
    0.1100

[Diana Lutz]

This works perfectly for this data set.

I looked into ismembertol and the 0.1 tolerance you set will only work for this data set.

This was just an example set for me, my actual data has vastly different x-values from y-values ( ex. x = 49.05 y = 0.1014). What should I do in this case when I can't set a tolerance?

[madhan ravi]

https://in.mathworks.com/help/matlab/ref/uniquetol.html

[Diana Lutz]

I think mucking around with the uniquetol will solve my issue. Thank you!

[madhan ravi]

Anytime :) , if my answer helped you solve your problem make sure to accept the answer.

Answer 2

[Image Analyst]

The comparisons A < B1 or A > B2 each product a logical vector. So you need to do an AND operation element by element with &. You used && which takes two scalar variables. So this should work:

indexes = find(A < B1 & A > B2);

You will now get linear indexes (not logical since were using the find function) where BOTH of those conditions are true.

[Diana Lutz]

I get:

idx =

0×1 empty double column vector

when I change my code to idx = find(A < B1 & A > B2)

[Image Analyst]

Correct! With your data

A =

0.2200 0.1100

0.3300 0.1100

0.5500 0.6600

There is no element that is in the range 0.11 to 0.13 (non-inclusive), which would mean both less than 0.13 and greater than 0.11.

If you want to include the 0.11 you can use >= instead of >

indexes = find(A <= B1 & A >= B2)