Re: List Manipulation: Conditionally changing y value when x value meets some criteria

*To*: mathgroup at smc.vnet.net*Subject*: [mg109016] Re: List Manipulation: Conditionally changing y value when x value meets some criteria*From*: Bill Rowe <readnews at sbcglobal.net>*Date*: Sat, 10 Apr 2010 06:54:37 -0400 (EDT)

On 4/9/10 at 3:31 AM, cjkphd at wi.rr.com (Charles Koehler) wrote: >I joined the data using: >pts=MapThread[{##1}&,{x,y}] While this will clearly work and there is nothing wrong with it, it seems to me more direct and clearer to do Transpose@{x,y} or even MapThread[List, {x,y}] >I assumed that by testing the x value using #[[1]], I could change >the value of y using #[[2]] as shown below. If no manipulation was >required based on the value of x, I would keep that point unchanged, >but I'm definitely missing something. >filtered=If[a<#[[1]]&<b,#[[2]]&=0],{#[[1]],#[[2]]}&,pts] >a and b are the range of x values One way to accomplish what you want would be to use pattern matching as follows: In[28]:= x = RandomReal[1, 10]; y = RandomReal[2, 10]; Sort[Transpose[{x, y}]] /. {a_?(.2 < # < .8 &), b_} :> {a, 0} Out[30]= {{0.0761041, 1.91884}, {0.129938, 0.115834}, {0.304408, 0}, {0.439366, 0}, {0.505744, 0}, {0.58412, 0}, {0.616887, 0}, {0.672258, 0}, {0.808959, 0.600491}, {0.827083, 1.27203}} Here, I sorted the x,y pairs simply to make it easy to see the output has 0 for y whenever x is between the two specified values.