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Re: Apply function to parts of a list

  • To: mathgroup at smc.vnet.net
  • Subject: [mg86242] Re: [mg86224] Apply function to parts of a list
  • From: "Thomas Dowling" <thomasgdowling at gmail.com>
  • Date: Fri, 7 Mar 2008 02:23:48 -0500 (EST)
  • References: <200803060759.CAA29253@smc.vnet.net>

Hello,

I am sure you will get many replies!

Nevertheless ...

list = {{x1, y1}, {x2, y2}, {x3, y3}, {xn, yn}}

1. Using  Apply

{2 #1 , #2 } & @@@ list

Out[34]= {{2 x1, y1}, {2 x2, y2}, {2 x3, y3}, {2 xn, yn}}

or

Apply[{2 #1 , #2 } &, list, {1}]

2. Replacement rules can sometimes be convenient.

list /. {x_,  y_ } -> {2 x, y }

I look forward to reading the (many?) other suggestions ...

Tom Dowling

On Thu, Mar 6, 2008 at 7:59 AM, guerom00 <guerom00 at gmail.com> wrote:

> Hi all,
>
> Very often, I find myself having datas to plot of this form :
>
> data={{x1,y1},{x2,y2},{x3,y3}...{xn,yn}}
>
> So, very conventional : a list of abscissa and ordinate. Now, let's say I
> want to multiply by 2 all my ascissa. Right now, I write :
>
> MapAt[2*#&,data,Table[{i,1},{i,1,Length[data]}]]
>
> It's OK but I isn't there another way to achieve this as I find this
> rather "involved" for such a simple thing ?
>
> Thanks in advance.
>


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