cumulative sum of an array

Hi, so I have an array,b, I need to find the cumulative sums for every 5 values.

To calculate the cumulative sum S of an array a with 5 values

 b=[1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0];
a=[1 2 3 4 5];
amean=mean2(a);
S=zeros([1 length(a)]);
S(1)=a(1)-amean
for i=2:5
  S(i)=S(i-1)+(a(i)-amean)
end
S=-2    -3    -3    -2     0

The result for b should look like S = -2 -3 -3 -2 0 0 1 3 6 0 -2 -3 -3 -2 0 0 1 3 6 0

[James Tursa]

What is your question? For the given b, what would be your desired output?

[Lanceric Tse]

The desired output with be an array S, which contains the cumulative sums of every 5 values.

The code under the %% is how I would get the cumulative sum of an array of 5 values

Answer 1

[Matt J]

   br=reshape(b,5,[]);

   S=reshape(  cumsum(br-mean(br))   ,1,[])

[James Tursa]

And, for older versions of MATLAB

S = reshape(  cumsum(bsxfun(@minus,br,mean(br)))   ,1,[])

Answer 2

[dpb]

>> N
N =
     5
>> S=sum(reshape(b,[],length(b)/N))
S =
    15    30    15    30
>> 

>> S=cumsum(reshape(b,[],length(b)/N))
S =
     1     6     1     6
     3    13     3    13
     6    21     6    21
    10    30    10    30
    15    30    15    30
>>

[Lanceric Tse]

I'm looking for the cumulative sum, not sum

[dpb]

Sorry, typo...the fix should be obvious... :)