Re: How Do You Reduce Multiple Elements in a List?

*To*: mathgroup at smc.vnet.net*Subject*: [mg33889] Re: How Do You Reduce Multiple Elements in a List?*From*: Erich Mueller <emueller at pacific.mps.ohio-state.edu>*Date*: Sun, 21 Apr 2002 06:14:27 -0400 (EDT)*Organization*: Ohio State University*References*: <a9r3ve$ltc$1@smc.vnet.net>*Sender*: owner-wri-mathgroup at wolfram.com

reduce[lst_] := {First[#], Length[#]} & /@ Split[lst] On Sat, 20 Apr 2002, Bob Harris wrote: > Howdy, > > This seems like such a simple thing, yet I've search through the big book > trying to figure it out. Perhaps someone can help me... > > Given a list of integers that generally contains the same number many times, > I'd like to reduce it to a list that just gives me the number/count pairs. > For example, I'd like to convert the list > {1, 1, 1, 1, 1, 2, 2, 2, 4, 4, 4, 4, 4, 4} > into > {{1,5}, {2,3}, (4,6}} > > Is there a built-in function to do this? Seems like a histogramming > operation, but I get no useful matches from ?*Hist*. > > Thanks, > Bob H > > H>