Re: second simple problem

*To*: mathgroup at smc.vnet.net*Subject*: [mg99698] Re: second simple problem*From*: Peter Pein <petsie at dordos.net>*Date*: Mon, 11 May 2009 06:26:29 -0400 (EDT)*References*: <gu666q$9tf$1@smc.vnet.net>

Francisco Gutierrez schrieb: > Dear sirs: > I have the following list: > ex={1,5,7,4,"M",6,7,8,9,1,"M",3} > I want to replace the M's in the following way: the first M by 5, and the second by2. > Thus I have a replacement list > rL={5,2} > The problem is to get ={1,5,7,4,5,6,7,8,9,1,2,3} > How can I do this in the most general form (for any length of ex and any number of values of "M")? > Thanks > Francisco > Hi Francisco, sorry for not answering. Can anyone please explain, why the "obvious" Fold[Replace[#1, "M" -> #2] &, ex, {a, b}] leads to an unchanged "ex"? It is nearly 3 am and I guess it is better to go to sleep, than to try to solve this one. Good night to all, Looking forward a solution, Peter.