Re: First nonzero in list

*To*: mathgroup at smc.vnet.net*Subject*: [mg110862] Re: First nonzero in list*From*: "gianpf" <jean.pellegri at orange.fr>*Date*: Thu, 8 Jul 2010 20:34:32 -0400 (EDT)*References*: <201007080713.DAA07701@smc.vnet.net> <i14ai8$g0d$1@smc.vnet.net>

Salut In : Last[Position[th, t : _Integer /; Not[t == 0]]] Out : 25 where th = {227, 342, 527, 0, 670, 730, 703, 0, 0, 649, 687, 614, 570, 501, 462, 402, 325, 254, 189, 99, 81, 36, 9, 8, 3, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0} Ciao jean "Leonid Shifrin" <lshifr at gmail.com> a =E9crit dans le message de news:i14ai8$g0d$1 at smc.vnet.net... > > Hi Steve, > > Here are a couple of ways: > > In[6]:= > inp = {227, 342, 527, 0, 670, 730, 703, 0, 0, 649, 687, 614, > 570, 501, 462, 402, 325, 254, 189, 99, 81, 36, 9, 8, 3, 0, 0, 0, 0, > 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, > 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0}; > > In[8]:= inp /. {x___, 0 ..} :> Length[{x}] > > Out[8]= 25 > > In[10]:= Length[inp] - LengthWhile[Reverse[inp], # == 0 &] > > Out[10]= 25 > > The first solution is more elegant but impractical for large lists. The > second is reasonably efficient also for large lists. There are many mor= e > solutions of course. > > Hope this helps. > > Regards, > Leonid > > On Thu, Jul 8, 2010 at 11:13 AM, S. B. Gray <stevebg at roadrunner.com> > wrote: > >> I have lists such as >> >> th = {227, 342, 527, 0, 670, 730, 703, 0, 0, 649, 687, 614, 570, 501= , >> 462, 402, 325, 254, 189, 99, 81, 36, 9, 8, 3, 0, 0, 0, 0, 0, 0, 0, >> 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, >> 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0} >> >> and I want to find the position of the last nonzero element (e.g. 3 at >> position 25). Trivial, but some poking around did not reveal a neat wa= y. >> >> Anyone? Thank you. >> >> Steve Gray >> >>

**References**:**First nonzero in list***From:*"S. B. Gray" <stevebg@ROADRUNNER.COM>