[scilab-Users] Emulate Matlab's ismember function in Scilab

[Samuel Gougeon]

Hi,

----- Message d'origine -----
De : Sébastien Bihorel
Date : 08/11/2009 12:29:
> Dear Scilab users,
>
> Is there an easy method to emulate the Matlab ismember function to 
> match numerical vectors to one another? I've  tried several things 
> with intersect but it does not seem to give consistent results.
>
> Here is a section of the Matlab help about ismember:
> [tf, loc] = ismember(A, S, ...) returns an array loc containing the 
> *highest *index in S for each element in A that is a member of S.
>
>
> Here is an example of Scilab code that I tried
> a = [5 3 1 7 2 9 2 6 4 1 3 6 8 0 1 4];
> b=1:5;
> [v,ka,kb]=intersect(a,b,'c');
>
> Surprisingly, ka is a mix of low, middle or high indexes... There must 
> a logic behind that, but I do not see the pattern.
>
>
> I am looking to extract only the highest indexes. Any help would be 
> appreciated.
>
> Sebastien 
Here is a function that works like Matlab for giving loc :
-----------
function loc = ismember(A,S, highest)
   // loc = ismember(A, S, highest)
   //
   // A : Matrix of booleans, integers, reals, complexes, polynomes
   // S : Matrix of same datatype than S
   // highest : Scalar boolean
   //
   // ismember() returns a matrix loc of A's format. loc(i,j) = linear
   //  index in S of the first (highest ==%F) | last (highest==%T)
   //  occurrence of A(i,j). Zero is returned in A(i,j) if no occurrence 
is found
   //
   LA=length(A);
   LS=length(S);
   A2=matrix(A,LA,1)*ones(1,LS) ;
   S2=(matrix(S,LS,1)*ones(1,LA)).' ;
   d01  =double(A2==S2);
   S_ind=ones(LA,1)*(1:LS);
   tmp=d01.*S_ind;
   if highest,
       tmp2=max(tmp,'c');
   else
       tmp(tmp==0)=%inf;    // removes zeros as min values
       tmp2=min(tmp,'c');
       tmp2(tmp2==%inf)=0;
   end
   loc=matrix(tmp2,size(A));
endfunction
--------
ismember() works with any datatype, as long as elements
can be multiplied by reals and compared each other with "==".

A test with reals gives:
-->A,S
 A  =
 
    7.    3. 
    2.    0. 
    8.    1. 
 S  =
 
    5.    8.    0.    4. 
    3.    4.    7.    7. 
    3.    6.    6.    2. 
    7.    5.    5.    8. 
 
-->ismember(A,S,%f)
 ans  =
 
    4.     2. 
    15.    9. 
    5.     0. 
 
-->ismember(A,S,%t)
 ans  =
 
    14.    3. 
    15.    9. 
    16.    0. 

HTH,

Regards
Samuel

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