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Re: Problem with the 'if' command

  • To: mathgroup at smc.vnet.net
  • Subject: [mg96625] Re: Problem with the 'if' command
  • From: Albert Retey <awnl at gmx-topmail.de>
  • Date: Tue, 17 Feb 2009 06:28:33 -0500 (EST)
  • References: <gncme2$fid$1@smc.vnet.net>

mathandpi wrote:
> Hi everyone,
> I'm a new Mathematica user so I may be missing something fairly obvious, but I'm having trouble with the 'if' command.
> I'm writing a function that is supposed to return the median of a list (I know such a function already exists, but I need to create one myself).
> 
> What I have is:
> 
> newMedian[list_] := 
>  If[Length[list]/2 == 0, 
      ^^^^^^^^^^^^^^^^^^^
Could it be you want something like: Mod[Length[list],2]==0 or even
better EvenQ[Length[list]] here? Length[list]/2 == 0 will always return
false except when Length[list] == 0, or list === {} ...

>   1/2*(list[[(Length[list]/2) + 1]] + list[[(Length[list])/2]])
>   , list[[(Length[list] + 1)/2]]]
> 
> if the list has an off number of members (condition is false), it evaluates as expected.  If it's even, however,
> 

> It seems likes its actually evaluating the false part of the code (trying to find the 5/2'ith element in a list), even though the condition is true.
> 

hth,

albert


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