Re: Need to reduce 2 lists so that only {x,y} pairs with same x remain

*To*: mathgroup at smc.vnet.net*Subject*: [mg24180] Re: [mg24134] Need to reduce 2 lists so that only {x,y} pairs with same x remain*From*: BobHanlon at aol.com*Date*: Wed, 28 Jun 2000 22:51:00 -0400 (EDT)*Sender*: owner-wri-mathgroup at wolfram.com

In a message dated 6/28/2000 2:39:53 AM, materialsscientist at my-deja.com writes: >I have 2 lists of data: > >for example >data1={{1,1},{1.5,1.5},{2,2},{3,3},{4,4},{5,5}} > >data2={{1,2},{2,3},{3,4},{4,5},{6,7},{7,8}} > > >I want to do a point by point comparision, so I >need to reduce both data1 and data2 so that >common x data in the {x,y} pairs for each list >remain. > >Thus the lists should look like this: > >data1={{1,1},{2,2},{3,3},{4,4}} >data2={{1,2},{2,3},{3,4},{4,5}} > >What function(s) would to something like this? > data1 = {{1, 1}, {1.5, 1.5}, {2, 2}, {3, 3}, {4, 4}, {5, 5}}; data2 = {{1, 2}, {2, 3}, {3, 4}, {4, 5}, {6, 7}, {7, 8}}; data1 = Select[data1, MemberQ[First[Transpose[data2]], #[[1]]] &] {{1, 1}, {2, 2}, {3, 3}, {4, 4}} data2 = Select[data2, MemberQ[First[Transpose[data1]], #[[1]]] &] {{1, 2}, {2, 3}, {3, 4}, {4, 5}} Bob Hanlon