speed optimization in "for" loops

Hi,

I have an experiment with 864 trials. I have an array named Edf_Trials3, with data of saccadic eye movements during the entire experiment. In some trials I have more than one eye movement, in others there is none.

I have an other array, named Time_EndPpt6, with the time of the stimuli presentation in each trial.

I would like to add the time of the stimuli presentation in the former array "Edf_Trials3", on the same line of the corresponding trial.

For that i'm using 2 loops but it's very very long.

Could you help to simplify my code in order to boost the process ?

I add the two arrays. this is my code:

for (j=1:height(Edf_Trials3))
    for(i=1:length(Time_EndPpt6))
        if (Edf_Trials3.Trial(j)==i)
            Edf_Trials3.EndTime_of_Ppt(j)=Time_EndPpt6(i);
        end
    end
end

Thanks for your help

[Jan]

I'd omit the strange parentheses for the for and if commands. It works, but does not look Matlabish.

Answer 1

[Jan]

The code overwrites Edf_Trials3.EndTime_of_Ppt(j) repeatedly. Then you can run the inner loop in backward direction and stop at the first match:

% [EDITED] pre-allocation
Edf_Trials3.EndTime_of_Ppt = zeros(1, height(Edf_Trials3));
for j = 1:height(Edf_Trials3)
   for i = length(Time_EndPpt6):-1:1
      if Edf_Trials3.Trial(j) == i
         Edf_Trials3.EndTime_of_Ppt(j) = Time_EndPpt6(i);
         break;   % Stop "for i" loop early
      end
   end
end

You could try a vectorization also:

% [EDITED] pre-allocation, typo: "m" -> "idx"
tmp = zeros(1, height(Edf_Trials3));
v   = 1:length(Time_EndPpt6);
for j = 1:height(Edf_Trials3)
  idx    = find(Edf_Trials3.Trial(j) == v, 1, 'last');
  tmp(j) = Time_EndPpt6(idx);
end
Edf_Trials3.EndTime_of_Ppt = tmp;

How large are the inputs? Can you post some relevant small example data?

[alice dormeuil]

Thanks for your answer,

In attachment you will find the examples of tables that I use. The array Time_EndPpt6 is 1x864 double array and the Edf_Trials3 is approximately 2 000 000 x9 table.

[Jan]

Unfortunately I cannot open MAT files currently, because I do not have access to Matlab. Is Edf_Trials3.EndTime_of_Ppt pre-allocated? If not, see my edited code. Is Edf_Trials3.Trial sorted? Do my suggests decrease the run-time already?

[alice dormeuil]

It's perfectly working now. Thanks a lot !