Re: Iterate through a list

*To*: mathgroup at smc.vnet.net*Subject*: [mg76931] Re: [mg76886] Iterate through a list*From*: János <janos.lobb at yale.edu>*Date*: Wed, 30 May 2007 05:21:41 -0400 (EDT)*References*: <200705290902.FAA03917@smc.vnet.net>

On May 29, 2007, at 5:02 AM, Nick Hoffman wrote: > Hello! I'm (somewhat) new to Mathematica and I need help to iterating > through a list and counting the occurrence of a number. > > My list looks like: > > {{1,0},{1,1},{2,x+x^2+x^4},{2,1+x+x^2+x^4},{4,x+x^2},{4,1+x+x^2}, > {4,x+x^4},{4,1+x+x^4},{4,x^2+x^4},{4,1+x^2+x^4},{4,x^3+x^4},{4,1+x^3= > +x^4},{4,x+x^2+x^3+x^4},{4,1+x+x^2+x^3+x^4},{5,x+x^3},{5,1+x+x^3}, > {5,x^2+x^3},{5,1+x^2+x^3},{5,x+x^3+x^4},{5,1+x+x^3+x^4},{5,x^2+x^3 > +x^4},{5,1+x^2+x^3+x^4},{8,x},{8,x^2},{8,x^3},{8,x^4},{8,1+x},{8,1 > +x^2},{8,1+x^3},{8,x+x^2+x^3},{8,1+x+x^2+x^3},{8,1+x^4}} > > > > The number that I would need to keep track of is the first in each > sub- > list. > > So for the first couple {{1,0},{1,1},{2,x+x^2+x^4},{2,1+x+x^2+x^4}, > {4,x > +x^2},........ > > I would need to keep track of 1,1,2,2,4........ > > It will not always be 1,2,4,5,8's. The numbers may be completely > different on each pass. Each sublist may be composed of more items > but the number that I need to keep track of will always be the 1st in > the sub-list. Any help or suggestions that you can give me will be > greatly appreciated. Thanks so much! Here is a newbie approach for this concrete list: In[2]:= First /@ lst Out[2]= {1, 1, 2, 2, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 5, 5, 5, 5, 5, 5, 5, 5, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8} J=E1nos ---------------------------------------------- Trying to argue with a politician is like lifting up the head of a corpse. (S. Lem: His Master Voice)

**References**:**Iterate through a list***From:*"Nick Hoffman" <hoffmannick@gmail.com>