cumulative sum of some columns of matrix

I have a 100 x 12 matrix of monthly climate data values.

I want to create a matrix with the cumulative sum of the three previous months.

How can I use cumsum() to get the cumulative sum by row of a certain number of specified columns, not the whole row?

Answer 1

[KL]

You seem to want to do cumsum along the second dimension, so trivial is to use

 res = cumsum(yourMat,2);

but this will produce the typical cumsum. If you want to add every 3 columns only for a specific row,

 yourRow = someval; %within your dimension range
 cs = 1:size(yourMat,2);
 cs1 = [1 1 cs(1:end-2)];
 res = arrayfun(@(x,y) sum(yourMat(yourRow,x:-1:y)), cs, cs1, 'uni',0);

[Roisin Loughnane]

That's closer!

For all rows, I want to add the previous three column values to each element of a matrix. So the result will also be a n x 12 matrix which I start with.

Sorry if I'm not being specific enough with my questions!

[KL]

Ah yeah, I made some changes to my answer. Note that, it's only for a specific row (yourRow). For all the rows, from the top of my head, I'd superimpose it with another arrayfun. It doesn't look very elegant but still works for you.

 res = arrayfun(@(z) arrayfun(@(x,y) sum(yourMat(z,x:-1:y)), cs, cs1, 'uni',0),1:yourRow,'uni',0)

[Roisin Loughnane]

It worked, thank you very much!

I used your code to loop over each row:

sst = table2array(sst(:,6:end));
res = zeros(size(sst));

for i = 1:length(sst)
    cs = 1:size(sst,2); 
    cs1 = [1 1 cs(1:end-2)]; % 1 1 : 10
    res(i,:) = arrayfun(@(x,y) sum(sst(i,x:-1:y)), cs, cs1);
end

Answer 2

[Birdman]

A=randi([1 10],100,12)
A(:,2:5)=(cumsum(A(1:100,2:5)')')

This two lines does the trick.