Re: Need a functional process for this.

*To*: mathgroup at smc.vnet.net*Subject*: [mg55598] Re: Need a functional process for this.*From*: Curt Fischer <tentrillion at gmail.NOSPAM.com>*Date*: Wed, 30 Mar 2005 05:29:05 -0500 (EST)*References*: <d2dpdm$lsd$1@smc.vnet.net>*Sender*: owner-wri-mathgroup at wolfram.com

Steve Gray wrote: > I have two lists, aa and bb. aa has the general form {2,5,7,9,11,...} > (or{{2},{5},{7},{9},{11},...}), and bb has the general form {{6,4},{9,2},{5,6},{3,8},.... If either > the first or second element in any sublist (pair of integers) of bb matches any element in aa, I > want to delete that sublist from bb. In the above example, neither member of {6,4} or {3,8} belongs > to aa, while at least one element of {9,2} and {5,6} belongs to aa, so bb becomes {{6,4},{3,8}}. If > aa had only one element, for example 7, I could do bb=Delete[bb,Position[bb,{x_,7}|{7,y_}]], but I > don't know how to do it for several values instead of just "7" without using a procedural loop. > What is a good functional way to do this? > Thank you for any tips. > > Steve Gray Here's my method. It creates a pure function Position[bb,{x_,#}|{#,y_}]& that it maps onto the list aa. This gives a list of the positions to be eliminated, but if a given element of aa doesn't cause any eliminations, this mapping leaves an unwanted empty sublist {} as an element of our larger list. The replacement rule //.{x___,{},y___}->{x,y} gets rid of those. I have a feeling there is a better solution that involves DeleteCases[], but I couldn't come up with anything off the bat. In[1]:= aa={2,5,7,9,11}; In[2]:= bb={{6,4},{9,2},{5,6},{3,8}}; In[3]:= bb=Delete[bb,(Flatten@Position[bb,{x_,#}|{#,y_}]&/@aa)//.{x___,{},y___}->{x,y}] Out[3]= {{6,4},{3,8}} -- Curt Fischer