how can i store a value of a calculation in a loop

Hi I have the following loop.

for k=1:length(hplid)
x=hplid(k);
q=sort(latency(hpl==x));
size(q);
figure;
plot(q,(1:numel(q))/numel(q))
title(['HPL ', num2str(x), ' Latency']);
xlabel('Seconds');
ylabel('% Percentile');
quant=interp1((1:numel(q))/numel(q),q,[.9 .95 .99]);
disp( '90%, 95% and 99% latency');
disp(quant); 
end

how can I store the value of quants to an array everytime the loop is exectued. Right quants only store the calculation of the last iteration of the loop.

Thank you

[Jan]

I have formatted your code using the "{} Code" button.

Answer 1

[Jan]

Store the vectors in a matrix using the loop counter as index:

quant = zeros(length(hplid), 3);  % Pre-allocate!!!
for k = 1:length(hplid)
   ...
   quant(k, :) = interp1((1:numel(q))/numel(q),q,[.9 .95 .99]);
   disp(quant(k, :)); 
end

Note: The line "size(q);" is useless.

[Ketan Bharucha]

I get the following error when I use your solution? any idea?

The following error occurred converting from duration to double: Undefined function 'double' for input arguments of type 'duration'. To convert from durations to numeric, use the SECONDS, MINUTES, HOURS, DAYS, or YEARS functions.

[Jan]

@Ketan: Please post the complete error message and the relevant part of the code. I can neither guess, which line causes the error, nor which variable has the type "duration". Note that the message contains a hint about the solution already.

Answer 2

[jean claude]

try this put it just before end of the loop

quantvalue=[];
quantvalue=[quantvalue quant];

[Walter Roberson]

This works, but is not efficient. Each time something is added on to the end of quantvalue, MATLAB has to look for new memory long enough to store the combined results, and copy the existing quantvalue over and then copy in the new values, and then throw away the existing quantvalue. When possible, it is much more efficient to allocate the memory to store all of the results and write them in as you go.

[jean claude]

yes that's totally right it's better to preallocate!