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MathGroup Archive 1998

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Re: Request for help: working with multi-level lists

  • To: mathgroup at smc.vnet.net
  • Subject: [mg13684] Re: Request for help: working with multi-level lists
  • From: "Allan Hayes" <hay at haystack.demon.cc.uk>
  • Date: Sat, 15 Aug 1998 04:39:16 -0400
  • References: <6qp3mc$al3@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

KCConnolly wrote in message <6qp3mc$al3 at smc.vnet.net>...
>I have a list of 10 elements, each of which is a list of three elements
>(let's say in each case an integer, a real number, and a string). I am
>looking for the most elegant way to select those first-level elements
>(i.e., the lists) whose integer element is equal to a particular value
>(let's say "1"), and then to obtain the mean of the real number
>elements of the lists selected.  This seems as if it should be simple,
>but everything I try leads to Part specification errors.  Any help
>would be greatly appreciated.
>

M[l_,k_]:=((Plus@@#)/Length[#])&[Cases[l, {k,r_,_}:>r]]

M[{{3,.3,"b"},{1,1,"c"},{3,.6,"d"}}, 3]

    0.45

Allan

------------------------------------------------------------- 
Allan Hayes
Mathematica Training and Consulting
Leicester UK
http://www.haystack.demon.co.uk
hay at haystack.demon.co.uk
voice: +44 (0)116 271 4198
fax: +44(0)116 271 8642



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