MATLAB: Combine rows generated in for loop

for loop

I use for loop to generate a row matrix of 1×3 per loop. For every three consecutive rows generated, I want to calculate the mean of each column of the 3 row matrices. It will give a result of one 1×3 row matrix. Let's say the for loop runs 210 times, there should be 70 rows, which are the row matrices of mean. Then, I want to group these 70 rows into one matrix.
How can I compute the mean of each column of every 3 generated row matrices? Then, combine row matrices of mean? Thanks for all advice!

Best Answer

Wait until you're done, then use the "magic" of Matlab internal storage order and rearranging...let's do a small example to show the idea--
>> x=rand(6,3)  % generate small sample data set...
x =
  0.7094    0.1190    0.7513
  0.7547    0.4984    0.2551
  0.2760    0.9597    0.5060
  0.6797    0.3404    0.6991
  0.6551    0.5853    0.8909
  0.1626    0.2238    0.9593
>> reshape(x,3,[])   % reshape based on number to average
ans =
  0.7094    0.6797    0.1190    0.3404    0.7513    0.6991
  0.7547    0.6551    0.4984    0.5853    0.2551    0.8909
  0.2760    0.1626    0.9597    0.2238    0.5060    0.9593
>> mean(ans)  % and take the mean; Matlab works by column by default
ans =
  0.5800    0.4991    0.5257    0.3832    0.5041    0.8498
>> reshape(ans,2,[])  % reshape back to three columns and voila!!!
ans =
  0.5800    0.5257    0.5041
  0.4991    0.3832    0.8498
>> [mean(x(1:3,:)); mean(x(4:6,:))]  % check it's right...
ans =
  0.5800    0.5257    0.5041
  0.4991    0.3832    0.8498
>>
OK, so to do the above in general
nAvg=3;
N=length(x);
nAvgMeans=reshape(mean(reshape(x,nAvg,[])),N/nAvg,[]);
Related Question