Re: What is the fastest way to threshold data?

*To*: mathgroup at smc.vnet.net*Subject*: [mg85931] Re: What is the fastest way to threshold data?*From*: "Kevin J. McCann" <Kevin.McCann at umbc.edu>*Date*: Thu, 28 Feb 2008 02:45:56 -0500 (EST)*Organization*: University System of Maryland*References*: <fq3af1$fot$1@smc.vnet.net>

Thanks to Carl Woll, Sseziwa Mukasa, Valeri Astanoff, and Bob Hanlon for responding to my query. I looked at each and they all work as expected, of course. The fastest is the suggestion due to Carl to use Clip: threshold = 0.75; data = RandomReal[{-1, 1}, {1000000, 3}]; Timing[data[[All, 3]] = Clip[data[[All, 3]], {threshold, Infinity}];] This runs in about 0.1s on my computer and is at least 10 times faster than the others. Thanks again. Kevin Kevin J. McCann wrote: > I have some 3d data {{x1,y1,z1},{x2,y2,z2},...} and I would like to set > the z-values to zero if they fall below zero. More generally, I would > like to set z to a threshold value if it is at or below a threshold. > This seems as though it should be an easy enough thing to do, but the > only way I have figured out is to parse out the z-vector, do > > mask=((#<thresh&) /@ zdata)/.True->0/.False->1; > > then > zvector = zvector*mask; > > and rebuild the {x,y,z} data. > > Kevin -- Kevin J. McCann Research Associate Professor JCET/Physics Physics Building University of Maryland, Baltimore County 1000 Hilltop Circle Baltimore, MD 21250