Re: Counting number of numbers in a large list between two valus

*To*: mathgroup at smc.vnet.net*Subject*: [mg114537] Re: Counting number of numbers in a large list between two valus*From*: Lyle Gordon <lgordon at gmail.com>*Date*: Tue, 7 Dec 2010 06:45:32 -0500 (EST)

Thanks everyone for your responses, it seems like Carl's and Fred's method with Total-Unitize-Clip is the fastest. Thanks very much, Lyle -- Lyle Gordon Department of Materials Science and Engineering Northwestern University 2220 Campus Drive Evanston, IL 60208 Tel: (847) 491-3584 Mobile: (847) 400-4071 lgordon at u.northwestern.edu On Mon, Dec 6, 2010 at 5:33 AM, Leonid Shifrin <lshifr at gmail.com> wrote: > Hi Lyle, > > Sorry - I misunderstood the problem. I thought you meant the positional > arrangement > of the numbers. Since you seem to be getting plenty of good answers, I > will not attempt > to correct myself with more code. > > > Regards, > Leonid > > > On Mon, Dec 6, 2010 at 5:57 AM, Lyle <lgordon at gmail.com> wrote: > >> Dear Listers, >> >> I have a large (5-20million) one dimensional list of real numbers and >> I want to count the number of entries in the list that lie between 2 >> specific values (x1, x2). I need to run the function for a number of >> different ranges. >> >> ie. number of list entries (l), where x1 <= l <= x2 >> >> I've tried: >> >> tallydata[{x1_, x2_}] := Count[data, x_ /; x1 <= x <= x2] >> >> that takes about 3-4 seconds >> >> and >> >> tallydata[{x1_, x2_}] := Length[Select[data, x1 <= # <= x2 &]] >> >> which takes a little bit longer. >> >> The best I've managed is (this last one might be off by 1 or 2 but >> this doesn't really matter to me): >> >> sorteddata = Sort[data]; >> nf = Nearest[sorteddata]; >> tallyrange[{x1_, x2_}] := >> First[Position[sorteddata, First[nf[x2]]]] - >> First[Position[sorteddata, First[nf[x1]]]] >> >> which takes between 1 and 2 seconds but I was hoping there might be a >> faster way to do this? >> >> Any help would be great! >> >> Thanks, >> Lyle Gordon >> >> Northwestern University >> >> >