Re: Counting number of numbers in a large list between two valus
- To: mathgroup at smc.vnet.net
- Subject: [mg114539] Re: Counting number of numbers in a large list between two valus
- From: "Kevin J. McCann" <Kevin.McCann at umbc.edu>
- Date: Tue, 7 Dec 2010 06:45:54 -0500 (EST)
- References: <idhjda$9f6$1@smc.vnet.net>
The fastest I got is data = RandomReal[UniformDistribution[{0, 1}], 10000000]; xmin = 0.5; xmax = 0.6; Timing[Total[UnitStep[(data - xmin)*(xmax - data)]]] {0.25, 1001405} On 12/5/2010 9:56 PM, Lyle 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 >