Re: K-Means Clustering

[John Darrington]

On Mon, Mar 14, 2011 at 12:22:36PM -0700, Mehmet Hakan Satman wrote:
     Hi John,
     
     1) I renamed the file as "quick-cluster.c"
     
     2. I added an entry to? "src/language/stats/automake.mk" for quick-cluster
     
     3. I removed the entry "UNIMPL_CMD ("QUICK CLUSTER", "Fast clustering")" 
from command.def file.

Thanks.  I tried some experiments with it.  It looks promising.  But there are 
some improvements
which can be made.
     
     4. Now cmd_quick_cluster can parse a command line like:
     
     QUICK CLUSTER x y z 
     ? ? ? /CRITERIA = CLUSTER(5) MXITER (100).
     
I inadvertently ran it with the wrong syntax (I typed just "QUICK CLUSTER." 
without any variables),
and it caused PSPP to crash.  You should check the return value of 
parse_variables_const 
and return an error if it fails.  See the code for the other procedures to see 
how to do this.

It also crashed if I omitted the /CRITERIA subcommand because your algorithm 
expects 
the number of groups is greater than 0.  The spss documentation says that
the CLUSTER and MXITER parameters both default to 2.  So you should initialise 
them accordingly.

     As
      I mentioned, i test my results with random data with uniform 
     distributed random values. It can not be considered as a comprehensive 
     work and should be tested with simulations. 

It's not my field of expertise, but I ran it with the following syntax:

input program.
        loop #i = 1 to 100000.
                compute x = rv.uniform (0, 1).
                end case.
        end loop.
        end file.
end input program.


QUICK CLUSTER ALL
        /CRITERIA = CLUSTER(3) MXITER (100).

and got :

Centers:
Center of Group 1: 0.499 
Center of Group 2: 0.833 
Center of Group 3: 0.165 

     
which is close to what I would expect (the centres are 1/6, 3/6 and 5/6).  Can 
you 
suggest some more comprehensive tests?


I have some general suggestions about the quick-cluster.c file:

1. The formatting style doesn't really fit the GNU way of doing things.  I 
recommend
   that you run the command "indent --gnu-style quick-cluster.c" to make it 
more consistent
   with the rest of the code.   You might want to read the information at 
   http://www.gnu.org/prep/standards/standards.html which explains how GNU 
software is 
   normally written and why we do it that way.

2. When compiling, I get a number of warnings.  Most of these are due to 
missing "static"
   qualifiers from the functions.

3. In PSPP we don't use the stdlib "malloc".  Instead we use "xmalloc" from 
gnulib.

4. Similarly, we don't use the srand and rand functions.  Use the gsl_rng_* 
functions.
   These are supposed to be better random number generators.
   See the file src/language/xforms/sample.c and/or the gsl manual for an 
example.


I'm looking forward to seeing the QUICK CLUSTER command integrated into PSPP.  
I tried
to find some examples of how spss presents its output for this command but I 
couldn't
find any.  Do you have any such examples or do you have access to a copy of 
pspp so that
we can see how users might expect to see the results?

Regards,


John




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