what can I do to prevent overwriting in for loop?

I have a data file recording a parameter every 1sec. I wrote a for loop to average each 60 rows to get 1 reading every 1min. what happened is that the code overwrite the results in the variable. help neede to correct the following code: for i=1:length(x) z=mean(x(i:i+59,:)) i=i+60 end variable z contain only one row. what can I do to prevent overwriting in for loop?

Answer 1

[Iain]

 z(i) = mean(x(i:i+59,:));

[zeinab]

for i=1:length(x)

z(i)=mean(x(i:i+59,:))

i=i+60;

end

??? In an assignment A(I) = B, the number of elements in B and I must be the same.

[Hikaru]

@zeinab,

Your code defined different values for i. First, you said i = 1,2,3, to whatever length of x is. But in the loop, you defined i=i+60 (I'm assuming this is for the purpose of averaging the 60 rows), but at the next loop, MATLAB would use i=2.

r = 1:60:length(x)
for i=1:
   z(i)=mean(x(r(i):r(i)+59,:))
end

[Iain]

z(i,:) = mean(x(i:i+59,:));

[zeinab]

@HIKARU, thanks for reply, and i will try this way. @lain, the loop doesn't stop :)

Answer 2

[Michael Haderlein]

for cnt=1:fix(length(x)/60)
z(cnt)=mean(x((cnt-1)*60+1:cnt*60));
end

But it's faster to not do it with a loop:

 z=mean(reshape(x(1:fix(length(x)/60)*60),60,[]));

You shouldn't use i as variable as it's also the imaginary unit. And don't change the value of the increment in the loop, this won't have the desired effect.

[zeinab]

thnks for reply but what are cnt,reshape,and fix?

[Michael Haderlein]

cnt is a variable, "counter". Better name than i. reshape is a function which changes the shape of an array without changing the number of elements. E.g. change a 4x1 into a 2x2 array. fix is cutting everything after the decimal separator. In case the length of x is not exactly a multiple of 60, the program would crash if this fix thing isn't taken.