MATLAB: Rowfun and sum of array elements based on start and stop position from another array

MATLABrowfun

Hi everybody,
I'm trying to sum values of a timetable based on start and endposition from another array. The results will be inserted in the timetable in a new column.
It works with loops but the size of my table makes it quite slow and since I use vectorization for other purposes, and it is quite fast, I only assume that there is a way to achive it with rowfun for example. But I tried several scenarios but it does not work.
Here is what I try to achieve through an example .
start position array : Start=[1;3;6]
stop position array : Stop=[2;5;8]
Values from timetable: Values=[10;20;10;30;50;40;80;20;10]
I want an output vector with the sum based on start and stop position, so a 3X1.
For example:
First result: sum of Values from position 1 to 2: 10+20=30
Second result: sum of Values from position 3 to 5: 10+30+50=90
Third result: sum of Values from position 6 to 8: 40+80+20=140
So, how to achieve that simple operation with rowfun?
Thanks.
Michel Rathé

Best Answer

It works with loops but the size of my table makes it quite slow
It shouldn't be. Even with several thousand table columns, a loop should still run in well less than 1 sec.
T=array2table(rand(1e4,3e3));
[M,N]=size(T);
    
Start=ones(1,N);
Stop=M*Start; %Worst case
matrix=table2array(T);
result=nan(1,N);
tic
for i=1:N
    
    result(i)=sum(matrix(Start(i):Stop(i),i));
    
end
toc
Elapsed time is 0.068844 seconds.
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