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Re: How to get sub-list elements at certain position in a long list

  • To: mathgroup at smc.vnet.net
  • Subject: [mg123096] Re: How to get sub-list elements at certain position in a long list
  • From: Armand Tamzarian <mike.honeychurch at gmail.com>
  • Date: Wed, 23 Nov 2011 07:06:27 -0500 (EST)
  • Delivered-to: l-mathgroup@mail-archive0.wolfram.com
  • References: <jafuf7$rs7$1@smc.vnet.net>

On Nov 22, 9:44 pm, Gy Peng <hitphy... at gmail.com> wrote:
> Dear Experts,
>
> I have a list:
>
> {{{{2.5}, {3.8, 31}, {54.23, 46.263, 45.987}, *{-82.1476,** 5.17782,
> -205.36}*}, {{2.5}, {4.2, 30}, {233.835, 46.469,
>     46.819}, *{93.8625, -13.9818, -198.778}*}}, {{{2.5}, {4.1,30},
> {139.845, 15.719, 155.87}, *{93.6633,**4.46398, -205.432}*}, {{2.5}, {2.6 ,
> 32}, {113.381, 40.988,85.09}, *{90.1206, 16.9792, -205.314}*}}, {{{2.5},
> {3.1,30}, {113.858, 34.709, 87.567}, *{55.3298,**17.7214, -211.648}*},
> {{2.5}, {2.7, 30}, {110.54, 31.595,85.601}, *{-25.8558, 175.588, -121.105}*
>
> }}}
>
> How do I get each 4th sublist element in the last level? I mean, I want to
> get a list looks like:
> {*{-82.1476, **5.17782, -205.36}, **{93.8625, -13.9818, -198.778},**{90.1206,
> 16.9792, -205.314},**{55.3298,**17.7214, -211.648},**{-25.8558, 175.588,
> -121.105}}*
> which only includes every 4th element in the last level. Do I describe my
> question clearly?
>
> Better not to use any "For", simple Map or Thread method are preferred.
>
> Thank you very much!!!
> *
> *

It is best to use Part for this. I am assuming that the asterisks are
a legacy of a cut and paste?

yourList = {{{{2.5}, {3.8, 31}, {54.23, 46.263, 45.987}, {-82.1476,
     5.17782, -205.36}}, {{2.5}, {4.2, 30}, {233.835, 46.469,
     46.819}, {93.8625, -13.9818, -198.778}}}, {{{2.5}, {4.1,
     30}, {139.845, 15.719, 155.87}, {93.6633,
     4.46398, -205.432}}, {{2.5}, {2.6, 32}, {113.381, 40.988,
     85.09}, {90.1206, 16.9792, -205.314}}}, {{{2.5}, {3.1,
     30}, {113.858, 34.709, 87.567}, {55.3298,
     17.7214, -211.648}}, {{2.5}, {2.7, 30}, {110.54, 31.595,
     85.601}, {-25.8558, 175.588, -121.105}}}}

yourList[[All, All, -1]]

or

Flatten[yourList[[All, All, -1]], 1]

Mike



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