Pattern matching
- To: mathgroup at smc.vnet.net
- Subject: [mg33912] Pattern matching
- From: John Leary <leary at paradise.net.nz>
- Date: Tue, 23 Apr 2002 07:13:22 -0400 (EDT)
- Sender: owner-wri-mathgroup at wolfram.com
Greetings
Can you help me please - there must be a simple solution to this problem,
but I can't find it.
From a list of character strings and a list of templates, I need to
produce a list of all strings that match any of the templates. For example:
listData={"18K0F3C--" , "2K40GXX--" , "400HGXX--" , "5M00G1F--" , "960KG1D--"}
listTemplates={"???H?????" , "???K?????"}
result={"400HGXX--","960KG1D--"}
In the templates, ? is a wild-card that represents a single character.
The data strings contain only alpha-numeric characters and hyphens - no
other characters.
There are no special requirements for the result: duplication and random
order are acceptable.
I searched the MathGroup archive and found a very useful function that does
exactly what I want, but it works only on individual strings, not lists of
strings (msg00051):
QMMatchQ[s_String, p_String] := MatchQ[Characters[s], Characters[p] /. "?"
-> _ ]
I tried to use it in the following way, but the result is a list of the
matching templates, not the matching strings :
QMMatchQ[s_String, p_String] := MatchQ[Characters[s], Characters[p] /. "?"
-> _ ]
SetOptions[Intersection, SameTest -> (QMMatchQ[#1,#2]& )];
result=Intersection[listData,listTemplates]
{"???H?????","???K?????"}
It ought to be a small step from there to the result that I need, but I
can't find a simple solution.
One alternative approach would be a Do loop:
b={};
Do[b=Append[b,Select[listData,QMMatchQ[#,listTemplates[[n]]]&]],{n,1,Length[listTemplates]}]
This works but seems to be very slow for large lists. In the real case,
listData can be very large - up to 250,000 elements - and the Do loop
approach doesn't seem to be optimum.
I would be very grateful for your help.
Regards
John Leary