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

*To*: mathgroup at smc.vnet.net*Subject*: [mg114513] Re: Counting number of numbers in a large list between two valus*From*: "Carl K. Woll" <carlw at wolfram.com>*Date*: Mon, 6 Dec 2010 06:13:05 -0500 (EST)

On 12/5/2010 8:57 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 > Here's one possibility: data = RandomReal[1, 10^7]; In[206]:= Total@Unitize@Clip[data, {.2, .3}, {0, 0}] // Timing Out[206]= {0.14, 1000695} Carl Woll Wolfram Research