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MathGroup Archive 2005

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Re: List element extraction

  • To: mathgroup at smc.vnet.net
  • Subject: [mg53486] Re: [mg53470] List element extraction
  • From: Andrzej Kozlowski <akoz at mimuw.edu.pl>
  • Date: Fri, 14 Jan 2005 08:54:32 -0500 (EST)
  • References: <200501130812.DAA03802@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

On 13 Jan 2005, at 09:12, Trinanjan Datta wrote:

> How do I extract the x values from the following list and divide them
> by 2:
>
> {{120.664, {x -> -4.64844}}, {
>         118.131, {x -> -4.4542}}, {115.479, {x -> -4.25828}}, {
>         112.697, {x -> -4.06053}}, {109.766, {x -> -3.8606}}, {
>         106.666, {x -> -3.65812}}, {
>   103.372, {x -> -3.45257}}, {99.8501, {x -> -3.24323}}, {
>   96.0571, {x -> -3.02915}}, {
>         91.9343, {x -> -2.80902}}, {87.3996, {x -> -2.58106}}, {
>         82.3355, {x -> -2.34305}}, {76.5712, {x -> -2.09251}}, {
>         69.8594, {x -> -1.8273}}, {61.8567, {x -> -1.54659}}, {
>         52.1348, {x -> -1.25235}}, {40.3287, {x -> -0.952531}}, {
>         26.7404, {x -> -0.66784}}, {13.703, {x -> -0.434276}}, {
>         5.08285, {x -> -0.270745}}, {1.45243, {x -> -0.152066}}}
>
>

Let

ls = {{120.664, {x -> -4.64844}}, {118.131, {x -> -4.4542}}, {115.479, 
{x -> \
-4.25828}}, {112.697, {
             x -> -4.06053}}, {109.766, {x -> -3.8606}}, {106.666, {x -> 
\
-3.65812}}, {103.372, {x -> -3.45257}}, {99.8501, {x -> -3.24323}}, 
{96.0571, \
{x -> -3.02915}}, {91.9343, {x -> -2.80902}}, {
       87.3996, {x -> -2.58106}}, {82.3355, {x -> -2.34305}}, {
       76.5712, {x -> -2.09251}}, {
             69.8594, {x -> -1.8273}}, {61.8567, {x -> -1.54659}}, 
{52.1348, \
{x -> -1.25235}}, {40.3287, {x -> -0.952531}}, {26.7404, {x -> 
-0.66784}}, {
       13.703, {x -> -0.434276}}, {5.08285, {x -> -0.270745}}, {
       1.45243, {x -> -0.152066}}};

then



(x /. Cases[ls, {_Rule}, Infinity])/2


{-2.32422, -2.2271, -2.12914, -2.030265, -1.9303,
   -1.82906, -1.726285, -1.621615, -1.514575, -1.40451,
   -1.29053, -1.171525, -1.046255, -0.91365, -0.773295,
   -0.626175, -0.4762655, -0.33392, -0.217138, -0.1353725,
   -0.076033}


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