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MathGroup Archive 2006

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Re: List Operations

  • To: mathgroup at smc.vnet.net
  • Subject: [mg65707] Re: List Operations
  • From: Bill Rowe <readnewsciv at earthlink.net>
  • Date: Sun, 16 Apr 2006 01:45:14 -0400 (EDT)
  • Sender: owner-wri-mathgroup at wolfram.com

On 4/14/06 at 4:32 AM, lectorz at mail.ru (LectorZ) wrote:

>My question:

>mylist={{1,a, b},{1,a, b},{1,a,
>b},{2,b,z},{2,b,z},{2,b,z},{2,b,z},....,{n,x,y},{n,x,y},{n,x,y},...{
>n,x,y}}

>The sublists are of different length.

>I need to calculate the product between the 2nd and 3rd element of
>every sublist (e.g. a*b) and then add them up according to the 1st
>element: sum of all products where the 1st element is 1, 2, ...n.

>The result should be a list like that:
>{{1,a*b+a*b+a*b},{2,b*z+b*z+b*z+b*z}, ...,{n, x*y+x*y+x*y+...+x*y}}

Try

{#[[1,1]],Rest[#[[2]]].Rest[#[[3]]]}&/@Partition[mylist,3]
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