reformulating for loop with vectorization or other approach - octave

问题

Is there any way to vectorize (or reformulate) each body of the loop in this code:

col=load('col-deau'); %load data

h=col(:,8); % corresponding water column
dates=col(:,3); % and its dates

%removing out-of-bound data
days=days(h~=9999.000);
h=h(h~=9999.000);
dates=sort(dates(h~=9999.000));

[k,hcat]=hist(h,nbin); %making classes (k) and boundaries of classes (hcat) of water column automatically

dcat=1:15; % make boundaries for dates
for k=1:length(dcat)-1 % Loop for each date class
    ii=find(dates>=dcat(k)&dates<dcat(k+1));% Counting dates corresponding to the boundaries of each date class
    for j=1:length(hcat)-1                                % Loop over each class of water column
        ij=find(h>=hcat(j)&h<hcat(j+1)); % Count water column corresponding to the boundaries of each water column class
        obs(k,j)=length(intersect(ii,ij));               % Find the size of each intersecting matrix
    end
end

I've tried using vectorization, for example, to change this part:

for k=1:length(dcat)-1        
    ii=find(dates>=dcat(k)&dates<dcat(k+1))  
endfor

with this:

nk=1:length(dcat)-1;
ii2=find(dates>=dcat(nk)&dates<dcat(nk+1));

and also using bsxfun:

ii2=find(bsxfun(@and,bsxfun(@ge,dates,nk),bsxfun(@lt,dates,nk+1)));

but to no avail. Both these approaches produce identical output, and do not correspond to that of using for loop (in terms of elements and vector size).

For information, h is a vector which contains water column in meters and dates is a vector (integer with two digits) which contains the dates in which the measurement for a corresponding water column was taken. The input file can be found here: https://drive.google.com/open?id=1EomLGYleaNtiGG2iV_9LRt425blxdIsm

As for the output, I want to have ii like this:

instead with the first approach I get ii2 which is very different in terms of value and vector size (I can't post the result because the vector size is too big).

Can someone help a desperate newbie here? I just need to reformulate the loop part into a better, more concise version.

If more details need to be added, please feel free to ask me.

回答1:

You can use hist3:

pkg load statistics
[obs, ~] = hist3([dates(:) h(:)] ,'Edges', {dcat,hcat});

来源：https://stackoverflow.com/questions/54282096/reformulating-for-loop-with-vectorization-or-other-approach-octave

标签

for-loop

vectorization

octave

bsxfun