Re: Tagged list processing

*To*: mathgroup at smc.vnet.net*Subject*: [mg86922] Re: [mg86891] Tagged list processing*From*: János <janos.lobb at yale.edu>*Date*: Wed, 26 Mar 2008 04:54:09 -0500 (EST)*References*: <200803250617.BAA10618@smc.vnet.net>

On Mar 25, 2008, at 2:17 AM, carlos at Colorado.EDU wrote: > This is related to a recent question. Best stated through an example. > I have two flat lists of equal length: > > tag={0,0,1,0,0, -3,0,0,0,0, 2,4,1,0,0}; > val={0,0,4,5,6, P,1/2,0,-3.0,a+4, 8,16.4,0,Sin[ang],Cos[ang]}; > > tag contains only integers whereas val can have numbers or > expressions that will (eventually) evaluate to a number. > > Task. Generate a pointer list to all nz values in tag, and a > corresponding list of values: > > nztag={3,6,11,12,13}; (* may be empty *) > nzval={4,P,8,16.4,0}; (* may be empty *) > > and also build the complementary lists > > ztag={1,2,4,5,7,8,9,10,14,15}; > zval={0,0,5,6,1/2,0,-3.0,a+4, Sin[ang],Cos[ang]}; > > Obviously ztag=Position[tag,0]; but which > form argument do I use for nztag in Position[tag,form]? > Can I build zval and nzval with Table for speed ? > (lists may contain 10^4 to 10^6 items) > > Constraint: must work in 4.0 thru 6.0 since some of my > remote students have legacy academic versions. Thanks. Here are some newbie approaches: First I would create a combined list with Inner: In[4]:=tagval = Inner[List, tag, val, List] Then, you can get nztag for example with Condition: > In[13]:= > Flatten[Position[tagval, > {a_, b_} /; a != 0]] > Out[13]= > {3, 6, 11, 12, 13} With the best, J=E1nos -------------------------------------------------------- The more money has to be spent to fix a problem, the more likely it is that the people with the money will agree to fix it. /Alex Satrapa/

**References**:**Tagged list processing***From:*carlos@colorado.edu