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