Re: List element replacement.

*To*: mathgroup at smc.vnet.net*Subject*: [mg52011] Re: [mg51980] List element replacement.*From*: Tomas Garza <tgarza01 at prodigy.net.mx>*Date*: Sun, 7 Nov 2004 01:03:28 -0500 (EST)*References*: <200411060707.CAA25986@smc.vnet.net>*Sender*: owner-wri-mathgroup at wolfram.com

Are the three lists the same Length? If that should be the case, e.g., In[1]:= initial = {0, 3, 4, 6, 8}; compare = {0, 0, 0, 3, 8}; replace = {0, 0, 0, 1, 7}; then the test whether "initial" has to change is based on MemberQ. All three elements of the test are True, and only in this case the replacements apply: In[4]:= (MemberQ[initial, #1] & ) /@ Union[compare] Out[4]= {True,True,True} The positions of the elements to be replaced in this case are In[5]:= replacements = Flatten[(Position[initial, #1] & ) /@ Union[compare]] Out[5]= {1,2,5} So, in general, the procedure is as follows In[6]:= If[Union[(MemberQ[initial, #1] & ) /@ Union[compare]][[1]] == True, initial[[replacements]] = replace[[ replacements]]]; That is, "initial" has been changed to In[7]:= initial Out[7]= {0,0,4,6,7} Tomas Garza Mexico City ----- Original Message ----- From: "Robert G. Wilson v" <rgwv at rgwv.com> To: mathgroup at smc.vnet.net Subject: [mg52011] [mg51980] List element replacement. > Et al, > > HELP, I tried this once before but what I received back I could not make > it work. > Therefore I am following the adage that if at first you do not succeed > then wait > awhile, rethink, restate and resubmit. > > I have three lists of objects, sorted but not unioned, that is there are > elements > which will be repeated. Let us label them 'initial' list, 'compare' list, > and > 'replace' list. If all of the elements in the 'compare' list, including > repeats, > are in the 'initial' list, then remove those elements and put in the > elements from > the 'replace' list. > > Thank you in advance, > > Bob. >

**References**:**List element replacement.***From:*"Robert G. Wilson v" <rgwv@rgwv.com>