Assigning indexes in an array and finding max values in a selected range

If we have X = time series data and signal in a 8000x 2 array (Matlab 2017b). The first column is time and the second column is signal of light absorbance. How can we find a maximum value in the selected range say from row 4000:5000 of the second column? Additionally, I would to like generate another column within X containing the index of each entry so that it becomes 8000x3 array. Thanks.

Answer 1

[Walter Roberson]

Assuming that X is a timeseries object (and not a Simulink time series):

rstart = 4000; rend = 5000;
[maxabs, maxidx] = max(X.Data(rstart:rend,2));
maxloc = rstart + maxidx - 1;
data_there = X.Data(maxloc,:);

It is not clear to me what the third column would be an index of?

[FW]

Thanks, I was looking for an index of the maximum value so that I can visually see where it is between 4000:5000. maxloc = rstart + maxidx - 1;

[Walter Roberson]

Is it correct that you want a new third column that is the index of each row so that when you find out the maxloc you can find the row visually in the table?

[FW]

Yes please.

[Walter Roberson]

X.Data(:,3) = 1:size(X.Data,1);