Workaround for subscript indices being non-integers and non-logicals

Hello,

I'm trying to return a submatrix with all rows that have a matching column value, but I'm receiving this error: Subscript indices must either be real positive integers or logicals.

The error is in line 22 of the attached code. I cannot round my array values to an integer, and I'm not sure if there is a more obvious or efficient way of sorting my data by a column value (column 5), reporting the median of column 2 values (distances) for all rows with matching values in column 1 (data from the same time point).

I am looking for advice on how to write the given function to do what I described above without indexing into a matrix using matrix with nonintegers. I am relatively new to MATLAB and there is likely a more efficient way to execute this, but I'm not sure what question to ask yet.

Please let me know if I can provide more information. Thank you for any help.

Answer 1

[Walter Roberson]

You do not show us the code for SortTime for the line

sorted_Time = SortTime(RelevantRows);

but we can predict that it is returning the sorted data, rather than the sort index. But later when you use

M2=sorted_Time;

AllTimes = M2(:,1);

then M2 will be the contents of the rows, not the indices. But then you do

TrackData = M2(AllTimes,:);

which assumes that what you are working with in AllTimes is indices, not direct values.

You need to go back and re-think which of your variables are to be indices and which of them are to be the contents of the array.

I suspect you are using the form

B = sortrows(A,column)

but you instead probably want to use the form

[B,index] = sortrows(A,column)

[jrb13]

Thank you! This really helped me think about what I'm doing. I was using B = sortrows(A,[column,column]). I didn't think about sorted_Time changing from indices to direct values, I thought I was just renaming sorted_Time for ease of writing/reading. I definitely don't think I would have caught/understood that I'm using AllTimes as indices in TrackData = M2(AllTimes,:); so thanks for that.

Answer 2

[Steven Lord]

There's no such thing as the 1.5th element of a vector or matrix. Perhaps you want to perform interpolation instead of or in addition to indexing?