MATLAB: Define variable-length matrix row sub-ranges using start and stop indices

bsxfunefficiencyindexperformancespeedsubsetvectorization

% Here's an interesting problem. I've tried to make it generic so your answers 
% (hopefully) will be more widely useful.
% 





% Context:
% - I have a latency sensitive program. 
% - I need to do some basic sub-referencing, such that I can
% - build up values in a matrix based on start and stop indices for each row.
% - I also want to be able to zero out values based on a non-index criteria.
% Assume I have:
sz          = 11;                               % length of rows
ind_ini     = [1 1 1 5 1 1]';                   % starting indices
ind_end     = [11 10 1 6 3 2]';                 % stopping indices
vals        = [1111 2222 3333 4444 5555 6666]'; % values to span index range
pts         = linspace(0,1,sz);                 % ref values for add'l criteria
rand_max    = [1 1 .3 .2 .1 .9]';               % max values for add'l criteria
% method 1
ind_logic = bsxfun(@ge,1:sz,ind_ini) & ...
            bsxfun(@le,1:sz,ind_end) & ...
            bsxfun(@le,pts,rand_max);
m         = bsxfun(@times,ind_logic,vals);      % matrix containing value spans

% method 2
n           = zeros(length(vals),sz);           % matrix containing value spans
for i = 1:length(vals)
    n(i,ind_ini(i):ind_end(i)) = vals(i);
    n(i,pts > rand_max(i)) = 0;
end
ind_logic     = n > 0;
all(all(m == n))
m
% m =
% 
%   Columns 1 through 6
% 
%         1111        1111        1111        1111        1111        1111
%         2222        2222        2222        2222        2222        2222
%         3333           0           0           0           0           0
%            0           0           0           0           0           0
%         5555        5555           0           0           0           0
%         6666        6666           0           0           0           0
% 
%   Columns 7 through 11
% 
%         1111        1111        1111        1111        1111
%         2222        2222        2222        2222           0
%            0           0           0           0           0



%            0           0           0           0           0
%            0           0           0           0           0
%            0           0           0           0           0
% Both of these methods provide the desired output, but they seem
% computationally inefficient. The loop is inefficient for obvious reasons, and
% the bsxfun approach seems like a lot of logical map generation for something 
% as "simple" as variable sub-ranges.
% What I would prefer is to have some non-iterative in-line method for
% referencing the sub-ranges of the rows in order to set them to the respective
% values. Something like:
m(ind_ini:ind_end) = vals
% where ind_ini and ind_end are the same vectors of indices. Since the lengths
% of these index-ranges are not consistent, "cells" came to mind. Something
% like:
subs = cellfun(@(x,y) x:y,num2cell(ind_ini),num2cell(ind_end),...
    'UniformOutput',0)
% subs = 
% 
%     [1x11 double]
%     [1x10 double]
%     [          1]
%     [1x2  double]

%     [1x3  double]
%     [1x2  double]
% but then I have the same problem when I try to refernce "m(subs) = vals"
% DOES ANYONE HAVE ANY CLEVER IDEAS?

Best Answer

Z = bsxfun(@times,vals,bsxfun(@le,pts,rand_max ));
mcell= arrayfun(@(j1)Z(j1,ind_ini(j1):ind_end(j1)),(1:length(ind_ini))','un',0);
EDIT
v = 1:sz;
m = cell2mat(arrayfun(@(i1)(vals(i1)*(+(ind_ini(i1)<=v&ind_end(i1)>=v&pts<=rand_max(i1))))',1:length(ind_ini),'un',0))'
about speed ... try the following:
v=1:sz;for i1 = length(ind_ini):-1:1, m(i1,:) = vals(i1)*(+(ind_ini(i1)<=v&ind_end(i1)>=v&pts<=rand_max(i1))); end;
my research
tic;v=1:sz;ind_logic = bsxfun(@ge,v,ind_ini) &bsxfun(@le,v,ind_end) & bsxfun(@le,pts,rand_max);m = bsxfun(@times,ind_logic,vals);toc
Elapsed time is 0.000668 seconds.
>> tic;v = 1:sz;m = cell2mat(arrayfun(@(i1)(vals(i1)*(+(ind_ini(i1)<=v&ind_end(i1)>=v&pts<=rand_max(i1))))',1:length(ind_ini),'un',0))';toc
Elapsed time is 0.001297 seconds.
>> tic,v=1:sz;for i1 = length(ind_ini):-1:1, m(i1,:) = vals(i1)*(+(ind_ini(i1)<=v&ind_end(i1)>=v&pts<=rand_max(i1))); end; toc
Elapsed time is 0.000113 seconds.
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