Combine rows generated in for loop

I use for loop to generate a row matrix of 1x3 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 1x3 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!

Answer 1

[dpb]

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,[]);

[Patrick]

Really a nice flow! Thanks for your help!