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

*To*: mathgroup at smc.vnet.net*Subject*: [mg114526] Re: Counting number of numbers in a large list between two valus*From*: Leonid Shifrin <lshifr at gmail.com>*Date*: Tue, 7 Dec 2010 06:43:29 -0500 (EST)

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 >