sum of two different data series

Hey all. I would like some help please on finding an efficient way of doing this:

I have two data series combined into one vector, so something like the below example

 data = 
 DataPoint DataIdx
 0.50       1
 0.25       1
 0.80       2
 0.10       1
 0.60       1
 0.50       2
 0.25       2
 0.50       2
 0.40       1
 0.10       1
 0.50       1

What I would like to do is add up all the data points per dataIdx, but preserve the order. So the output would be a "consolidated" vector which would look something like:

 output = 
 DataConsolidated DataIdx
 0.75             1
 0.80             2
 0.70             1
 1.25             2
 1.00             1

At the moment, I am using a for-loop that keeps a tally, but I hope there is a more elegant solution. I think this might lend itself well to an application of "accumarray", but I have not that much experience with this function. Any help pls?

Thanks! Hamad

[Image Analyst]

Maybe it's better, for code maintainability and ease of understanding it (especially later), if you just go with a simple intuitive for loop rather than some cryptic accumarray function that you don't understand. Simplicity has its benefits.

Answer 1

[Azzi Abdelmalek]

A=[0.50       1
0.25       1
0.80       2
0.10       1
0.60       1
0.50       2
0.25       2
0.50       2
0.40       1
0.10       1
0.50       1 ]
jj=[0; diff(A(:,2))~=0];
kk=cumsum(jj);
[~,id]=unique(kk);
out=[ accumarray(kk+1,A(:,1)) A(id,2)]

[Hamad]

Efficient, concise, and informative. Thanks very much! Hamad.

Answer 2

[Oleg Komarov]

You cannot use DataIdx directly as subs in accumarray() because in your example each streak of indices is treated as a separate accumulation block while the labeling is repeated, i.e. the 1s appear again after 2. You need to re-label the DataIdx and accumulate.

% Run-length encode the DataIdx:

    DataIdx   = [1,1,2,1,1,2,2,2,1,1,1];
    [val,len] = RunLength(DataIdx);

% Decode back, but with a progressive index, i.e. expand sequential positions by the len of each streak:

    subs = RunLength(1:numel(val),len)'

% Accumulate

   [val' accumarray(subs, DataPoint)]

PS. RunLength() is on the FEX by Jan Simon.

[Hamad]

Thanks very much Oleg!