integer strings decoding ... speed optimization

I have the following problem:

I need decode integer sequences "c" to char string messages "m" by following association:

numpos = 10 % ( = size(c,2)/2)
c = [3 4 1 1 4 2 5 2 3 3,1 1 1 1 2 2 2 3 3 3]

Each row of "c" represents 2*numpos integers, where first numpos parameters encoded position of

types = {'a' 'b@2' 'c@6' 'd@10' 'e@11'}

and second numpos parameters are applied only if type contains character '@' like this:

m = ' c:1@6 d:1@10 a a d:2@10 b:2@2 e:2@11 b:3@2 c:3@6 c:3@6'

My current solution is as follows:

function m = c2m(c,types)

numpos = size(c,2)/2;

F = cellfun(@(f) [' ' f], strrep(types,'@',':%d@'),'unif',0);
m = arrayfun(@(f,k) sprintf(f{1},k),F(c(:,1:numpos)),c(:,numpos+(1:numpos)),'unif', 0);
m = arrayfun(@(i) horzcat(m{i,:}), (1:numlines)', 'unif', 0)

end

and the testing code is as follows:

numlines = 10;
c = repmat([3 4 1 1 4 2 5 2 3 3,1 1 1 1 2 2 2 3 3 3],numlines,1);
types = {'a' 'b@2' 'c@6' 'd@10' 'e@11'};

m = c2m(c,types);

m =

    10×1 cell array

      {' c:1@6 d:1@10 a a d:2@10 b:2@2 e:2@11 b:3@2 c:3@6 c:3@6'}
      {' c:1@6 d:1@10 a a d:2@10 b:2@2 e:2@11 b:3@2 c:3@6 c:3@6'}
      {' c:1@6 d:1@10 a a d:2@10 b:2@2 e:2@11 b:3@2 c:3@6 c:3@6'}
      {' c:1@6 d:1@10 a a d:2@10 b:2@2 e:2@11 b:3@2 c:3@6 c:3@6'}
      {' c:1@6 d:1@10 a a d:2@10 b:2@2 e:2@11 b:3@2 c:3@6 c:3@6'}
      {' c:1@6 d:1@10 a a d:2@10 b:2@2 e:2@11 b:3@2 c:3@6 c:3@6'}
      {' c:1@6 d:1@10 a a d:2@10 b:2@2 e:2@11 b:3@2 c:3@6 c:3@6'}
      {' c:1@6 d:1@10 a a d:2@10 b:2@2 e:2@11 b:3@2 c:3@6 c:3@6'}
      {' c:1@6 d:1@10 a a d:2@10 b:2@2 e:2@11 b:3@2 c:3@6 c:3@6'}
      {' c:1@6 d:1@10 a a d:2@10 b:2@2 e:2@11 b:3@2 c:3@6 c:3@6'}

The code is still too slow for me, I am looking for any speed up. In this case the most significant fraction of CPU time is spent at built-in function "sprintf".

Typical realistic sizes of problem are:

   numpos ~ 30 ... 60
   numlines ~ 1e4 ... 1e5

Any idea?

Answer 1

[Michal]

Probably fastest and simplest solution, I found so far ... using latest new Matlab (>= R2016b) features, see function insertBefore and string datatype.

function m = c2m(c,types) 
     types = string(types);
     numpos = size(c,2)/2;
     a = c(:,1:numpos);
     b = c(:,(numpos+1):end);
     m = types(a);
     m = insertBefore(m,"@", ":" + b);
     m = join(m,2);
 end

[Jan]

Does this consider that some types as "a" do not get an element of b?

[Michal]

I am not sure, what do you mean exactly. Please clarify your question.

Answer 2

[Jan]

[EDITED] Consider all rows of c:

function m = c2m(c,types)
[s1, s2] = size(c);
numpos   = s2 / 2;
m        = cell(s1, 1);
typesF   = strrep(types, '@', ':%d@');  % types to format specifiers
hasNum   = ~strcmp(types, typesF);      % true if the type has a '%d'
for im = 1:s1
  c1      = c(im, 1:numpos);
  c2      = c(im, numpos+1:end);
  FmtSpec = sprintf(' %s', typesF{c1});        % Complete list of format specs
  m{im}   = sprintf(FmtSpec, c2(hasNum(c1)));  % All c2, if c1 has a number spec
end
end

UNTESTED - I have no Matlab currently.

[Michal]

c is (numlines x 2*numpos) integer matrix. Your code ignore that.

See my testing code.

[Jan]

But does it work correctly if c is a single row? It would be kind to provide this information, because I cannot run Matlab currently. The code is just written in the forum's interface.

I've edited the code to expand it to multi-row input.

A small speedup with https://de.mathworks.com/matlabcentral/fileexchange/26077-cstr2string:

% FmtSpec = sprintf(' %s', typesF{c1});  % Replace with:
FmtSpec = CStr2String(typesF{c1}, ' ', 'noTrail');

[Michal]

FmtSpec = CStr2String(typesF{c1}, ' ', 'noTrail');

should be

FmtSpec = CStr2String(typesF(c1), ' ', 'noTrail');

But the speed up with MEX file is only about a few percent.

[Michal]

Jan, thanks a lot for your help. Your code is very good. Especially the fact, that the for-loop is possible to simple transform to parfor-loop to get some additional speed-up without any re-programming.