Re: Count Function

*To*: mathgroup at smc.vnet.net*Subject*: [mg65556] Re: Count Function*From*: "Ray Koopman" <koopman at sfu.ca>*Date*: Fri, 7 Apr 2006 06:14:37 -0400 (EDT)*References*: <e1091t$ljd$1@smc.vnet.net>*Sender*: owner-wri-mathgroup at wolfram.com

Gregory Lypny wrote: > The syntax will be the death of me. > > Count[X[[All,14]], -9.] will tally how many elements in column 14 of > matrix X are equal to -9, but I can't for the life of me figure out > how to get how many are greater than -9. Any hint would be most > appreciated. > > Greg My earlier post omitted the really fast one. In[1]:= x = Table[Random[Integer,99],{1*^6}]; Timing@Count[x, x_/;x>14] Timing@Length@Select[x,#>14&] Timing[SparseArray[Boole@Positive[x-14]] /. SparseArray[_, _, _, p_] :> Length@p[[2, 2]]] Timing[SparseArray[UnitStep[x-15]] /. SparseArray[_, _, _, p_] :> Length@p[[2, 2]]] Out[2]= {2.17 Second,850268} Out[3]= {2.17 Second,850268} Out[4]= {1.1 Second,850268} Out[5]= {0.09 Second,850268}