Re: Better Way of Testing and Replacing List Elements?

*To*: mathgroup at smc.vnet.net*Subject*: [mg103993] Re: Better Way of Testing and Replacing List Elements?*From*: Januk <ggroup at sarj.ca>*Date*: Thu, 15 Oct 2009 07:15:05 -0400 (EDT)*References*: <hb3fus$lsk$1@smc.vnet.net>

There are many options. From fast to slow: xxx = RandomInteger[{-10, 10}, 10^6]; Use Clip: y2 = Clip[xxx, {0, \[Infinity]}]; // Timing Use UnitStep: y3 = (# * UnitStep[#])& @ xxx; // Timing Use pattern replacement: y4 = xxx /. {x_?(# < 0 &) :> 0}; // Timing Create a function: f[x_?(# < 0 &)] := 0 f[x_] := x y5 = f /@ xxx; // Timing Your original solution: y1 = ReplacePart[xxx, Position[Map[Negative, xxx], True] -> 0]; // Timing Create a piecewise function: g[x_] := Piecewise[{{x, x >= 0}}] y6 = g /@ xxx; // Timing Hope that helps, Januk On Oct 13, 11:18 pm, careysub <carey... at gmail.com> wrote: > The code below replaces the negative values in a list with zero, and > is an example of a type of operation I use a lot: > > xxx = {1, 2, 3, 4, 5, -6, -7, 8, 9, 10, -1, 11, 12}; > ReplacePart[xxx, Position[Map[Negative, xxx], True] -> 0] > > Is there a "better" way of doing this (fewer function calls, more > efficient)? > > My feeling is that I'm doing this in an awkward way.