Vectorize strcat and str2num for loop

I'm trying to speed up this for loop function. Basically want to to concatonate two integrers, but as the columns and frames variables contain different number of significant figures, I need to include leading zeros. I have tried using a decimal place to merge the values, but the rounding fails for large column/frame numbers. Is there any way I can speed up this for loop, or other efficient ways to do this?

nframes = 1800;
ncols = 801;

columns = 1:ncols;
frames = 1:nframes;
frames = repmat(frames,ncols,1);
columns = repmat(columns,1,nframes);
frames = frames(:);
columns = columns(:);
ID = zeros(1,nframes*ncols);
tic
for xx = 1:nframes*ncols
ID(xx) = str2num(strcat(sprintf('%03i',columns(xx)),sprintf('%04i',frames(xx))));
end
toc

Thanks.

[Jed Abanat]

That works great thank you!

[madhan ravi]

[comment moved to answer section]

Answer 1

[madhan ravi]

See if this is faster than a loop:

columns * 1e4 + frames