cellfunc vs cell2mat speed?

[Levente Torok]

Hi David and others

This is small speed test:

function t = test( s )

    t = time;
    c=cell( s, 1 );
    r = rand( 8, 1 );
    c{:,1} = r;
    cc = cell2mat( c );
    t = time - t;

end

octave:4> test( 1000 )
ans =  0.27966
octave:5> test( 10000 )
ans =  12.347
octave:6> test( 13000 )
ans =  26.865
octave:3> test( 16000 )
ans =  47.761
octave:4> test( 19000 )
ans =  83.082


As it seems, each adding of 3000 elements doubles the time it needs to convert cell to matrix.
I believe the slowness is due to the recursive scripting nature of the cell2mat.m function.
I thought I will write a small conversion program in C with limited capabilities for my own needs 
( ie. only c{i,1} =matrix will be handled ) but I am so much confused with the interface of the 
Cell class.


( NB: if I replace cell2mat with cellfun( c, "mean" ) I would get:
octave:10> test( 20000 )
ans =  8.0793
and this increases linearly with size of the cell array)
Thank you very much in advance,

Levente




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