Extracting a vlue from a matrix using a neighboring value as a reference

How would I go about extracting an indivdual value from column based on the max value from anothe row?

Say I have the following 2 x 5:

1 2 4 10 3

6 27 30 3 1

And I want to extract a value from Row 2, based on the column of the max value of Row 1. Which in this case would give me 3.

Answer 1

[Dyuman Joshi]

If you want the value corresponding to all occurences of the maximum value in row 1 -

%Input data
arr = [1  2   4   10  3  10
       6  27  30  3   1  5];

idx1 = arr(1,:) == max(arr(1,:));
val1 = arr(2, idx1)

val1 = 1×2

3 5

If you want the value corresponding to the first occurence of the maximum value in row 1 -

[~, idx2] = max(arr(1, :));
val2 = arr(2, idx2)

val2 = 3

[Alan Jurisich]

Hope you don't mind me reapeating it back. I want this to stick.

So i can use ~ to ignore creating a variable for the values, and just create the value for the index. Then max(arr(1, :)) will just search the first row.

Last, using the index variable (idx2) in the column position, MATLAB will just read the column portion of idx2. As in it wont get confused seeing what I assume would be a vector.

or would idx2 just equal the value of the column?

[Dyuman Joshi]

"So i can use ~ to ignore creating a variable for the values, and just create the value for the index."

Correct, it ignores the first output argument from the function.

"Then max(arr(1, :)) will just search the first row."

Correct.

"or would idx2 just equal the value of the column?"

Yes, idx2 is equal to the value of column, where the maximum of row 1 occurs for the 1st time.

%Input data
arr = [1  2   4   10  3  10
       6  27  30  3   1  5];

[~, idx2] = max(arr(1, :))

idx2 = 4

10 appears first in the 4th column of row 1.