Re: Converting a mapping into a well-defined function

*To*: mathgroup at smc.vnet.net*Subject*: [mg56532] Re: Converting a mapping into a well-defined function*From*: Peter Pein <petsie at arcor.de>*Date*: Thu, 28 Apr 2005 02:40:26 -0400 (EDT)*References*: <d4msni$257$1@smc.vnet.net>*Sender*: owner-wri-mathgroup at wolfram.com

Gilmar wrote: > Dear Mathematica User Friends: > > I need to build a module that takes a non-empty set A > (whose elements are 2-tuples), and appends (or not) those 2-tuples > to a set B according to the following criteria: > > (1.) if the abscissa of a 2-tuple in A is unique (among the abscissas > of all the other 2-tuples in A), then the module appends that 2-tuple > to the set B. > > (2.) if there are n 2-tuples in A that share the same abscissa, then > the module appends the first of those 2-tuples to B ("first" here means > the first of such n 2-tuple encountered, as you read A from left to > right),but does not append the rest to B. > > (3.) the module does not attempt to sort the set B, after the appending > process is completed. > > Example: > > If A = {{a,5},{b,27},{a,14},{c,4},{e,94},{b,6},{d,9},{e,4}} > > then > > B=Module[A]={{a,5},{b,27},{c,4},{d,9},{e,94}}. > > Another way to re-phrase the above example; > > if A defines a mapping: > > A(a)=5, A(b)=27, A(a)=14, A(c)=4, A(e)=94, A(b)=6, A(d)=9, A(e)=4 > > them the module converts the mapping A into a well-defined function: > > A(a)=5, A(b)=27, A(c)=4, A(d)=9, A(e)=94. > > Thank you for your help! > Hi, you say B shall not be sorted, but in your example it is? The corrected example can be obtained by: map2fun[lst_] := Fold[Join[#1, Complement[{#2}, #1, SameTest -> (SameQ @@ First /@ {##1} & )]] & , {}, lst]; A = {{a, 5}, {b, 27}, {a, 14}, {c, 4}, {e, 94}, {b, 6}, {d, 9}, {e, 4}}; map2fun[A] {{a,5},{b,27},{c,4},{e,94},{d,9}} b.t.w.: Module is a reserved Word in Mathematica. -- Peter Pein Berlin