Re: Pattern matching more than once
- To: mathgroup@smc.vnet.net
- Subject: [mg12096] Re: Pattern matching more than once
- From: Paul Abbott <paul@physics.uwa.edu.au>
- Date: Sat, 25 Apr 1998 01:30:28 -0400
- Organization: University of Western Australia
- References: <6hjqaa$2kj@smc.vnet.net>
ASARI Hirotsugu wrote: > I have been stuck with the following problem for about 10 days. I can't > think of an elegant solution. > > Input: Two lists, from some universal set Output: Many "spliced" lists > obtained from the input. > > e.g. {{a,b,c},{d,e,f}} --> {{a,b,c},{d,e,f}} (no common element) > > {{a,b,c},{d,b,f}} --> {{a,b,c},{d,b,f},{a,b,f},{d,b,c}} > > {{a,b,c,d,e},{f,b,g,d,h}} --> > {{a,b,c,d,e},{a,b,c,d,h},{a,b,g,d,e},{a,b,g,d,h}, > {f,b,c,d,e},{f,b,c,d,h},{f,b,g,d,e},{f,b,g,d,h}} I think that the following code: In[1]:=extendList[l_List]:= Module[{tr=Union/@Transpose[l]}, If[tr==Transpose[l],l,tr=Outer[List,Sequence@@tr]; Flatten[tr,Length[Dimensions[tr]]-2]]] which relies on Transpose (to pair up elements from each list) Union (to check for common elements) and Outer (to construct all allowed combinations) does what you want: In[2]:= extendList[{{a,b,c},{d,e,f}}] Out[2]= {{a,b,c},{d,e,f}} In[3]:= extendList[{{a, b, e}, {d, b, f}}] Out[3]= {{a,b,e},{a,b,f},{d,b,e},{d,b,f}} In[4]:= extendList[{{a,b,c,d,e},{f,b,g,d,h}}] Out[4]= {{a,b,c,d,e},{a,b,c,d,h},{a,b,g,d,e},{a,b,g,d,h}, {f,b,c,d,e},{f,b,c,d,h},{f,b,g,d,e},{f,b,g,d,h}} I also feel that there should be a cleverer pattern-matching solution, probably using ReplaceList ... Cheers, Paul ____________________________________________________________________ Paul Abbott Phone: +61-8-9380-2734 Department of Physics Fax: +61-8-9380-1014 The University of Western Australia Nedlands WA 6907 mailto:paul@physics.uwa.edu.au AUSTRALIA http://www.pd.uwa.edu.au/~paul God IS a weakly left-handed dice player ____________________________________________________________________