MATLAB: Intersect, Compare two columns or two matrix and extract common information

Question

Hi All,

I have a matrixe with 4 columns (A to D) or 1 to 4. I want to compare columns 2 and 4 and if a match is found, put the entire corresponding rows in a separate matrix called Match. Ex ample when it comes to row 2, under coulms 2 (B) AND 4 (D), the vaule 12.1 is common to both. Hence put this entire matching row in a new matrix which will become 12, 12.1, 12.4, 12.1

The idea is to extract information common to both columns 2 and 4, for each row and after finding this common information, include with them their associated information in coulmns 1 and 3. Please see attached im

I tried using the intersect function but it doesnt work the way I want it to.

Thanks very much.

Answer 1

Here's a demo you can follow. It identifies rows of a matrix 'data' where the value in column 2 exactly matches the value in column 4.

% demo, random data
data = randi(3,12,4); 
% Find rows where value in col 2 exactly matches value in col 4

isMatch = data(:,2)==data(:,4);
% Put those rows into a new matrix

newMat = data(isMatch,:); 

For floating decimals, 4.9999999 and 4.9999998 will not be an exact match. You can subtract the values from columns 2 and 4 and determine if the absolute value of their difference is less than some threshold you choose.

% Find rows where value in col 2 exactly matches value in col 4
isMatch = abs(data(:,2)-data(:,4)) < 0.0001; 
% Put those rows into a new matrix
newMat = data(isMatch,:);