Re: the Union of real numbers

*To*: mathgroup at smc.vnet.net*Subject*: [mg7029] Re: the Union of real numbers*From*: adams (Adam Strzebonski)*Date*: Fri, 2 May 1997 21:30:54 -0400 (EDT)*Organization*: Wolfram Research, Inc.*Sender*: owner-wri-mathgroup at wolfram.com

SameTest option allows to specify a function to be used by Union to decide which elements should be considered equal: In[1]:= N[{Pi, Pi+10^-10, Pi-10^-10}] Out[1]= {3.14159, 3.14159, 3.14159} In[2]:= Union[%] Out[2]= {3.14159, 3.14159, 3.14159} In[3]:= t = If[NumericQ[#1] && NumericQ[#2], Abs[N[#1 - #2]] < 10^-6, #1===#2]&; In[4]:= Union[%1, SameTest->t] Out[4]= {3.14159} Adam Strzebonski Wolfram Research In article <5k9gf9$m55 at smc.vnet.net> rustybel at foothill.net (Russell Towle) writes: > Hi, > > I am trying to apply the Union function to a list of real numbers, in which > many duplicates occur. However, small differences between the numbers > cause some of the duplicates to be retained instead of discarded. > > Suppose the list of real numbers is called k, my present work-around is as > follows: > > Union [ Rationalize [ k, 10^-6 ] ]. > > This does discard the duplicates. Is there a better method? > > Russell Towle > Giant Gap Press: books on California history, digital topographic maps > P.O. Box 141 > Dutch Flat, California 95714 > ------------------------------ > Voice: (916) 389-2872 > e-mail: rustybel at foothill.net > ------------------------------ > >