[OpendTect_Developers] (BufferStringSet) sorting

[Bert Bril]

Hi all,


In OpendTect, there are several tools for sorting arrays and sets. Most 
of them can be found in Algo/sorting.h . For large sets you may want to 
consider parallel sorting but I'll focus on simple smaller sets here.

As you know, very often the sorting is not the only thing you want - you 
also want to know the indexing. In OpendTect, these indexing arrays are 
simply arrays where arr[N] returns the index of the Nth element of the 
input array in the sorted output. You can obtain them using sort_coupled:

mAllocVarLenArr( int, idxs, sz );
mAllocVarLenArr( float, vals, sz );
for ( int idx=0; idx<sz; idx++ )
{
     vals[idx] = the_vals[idx];
     idxs[idx] = idx;
}
sort_coupled( vals, idxs, sz );

Some classes have a sort() function ready to use, like TypeSet and 
BufferStringSet. Because sorting of strings is something you often do to 
in combination with other sets (other BufferStringSet's, or IDs, or 
...), this class delivers a nice getSortIndexes() function. For example: 
sorting two sets for strings on the names in one of them (master/slave), 
you do:

int* idxs = getSortIndexes( master );
master.useIndexes( idxs );
slave.useIndexes( idxs );
delete [] idxs;

It's easy to see that the 'idxs' can be used for many other things. In 
loops, you will see expressions like 'arr[ idxs[idx] ]' .


/Bert

-- Bert Bril / OpendTect developer at dGB
-- mailto:Bert.Bril at opendtect.org , http://opendtect.org