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MathGroup Archive 2010

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Re: Apply a function to parts of a list

  • To: mathgroup at smc.vnet.net
  • Subject: [mg110319] Re: Apply a function to parts of a list
  • From: Peter Pein <petsie at dordos.net>
  • Date: Sun, 13 Jun 2010 04:10:35 -0400 (EDT)
  • References: <huvk7i$rtn$1@smc.vnet.net>

Am Sat, 12 Jun 2010 09:32:34 +0000 (UTC)
schrieb Rui <rui.rojo at gmail.com>:

> I have always done very ugly code when trying to do something
> seemingly simple and basic such as applying a function to subparts of
> a list. Simple example, I want to divide by 2 all the second elements
> of a list
> {{a, 5}, {b, 6}, ...}   -->  {{a, 5/2}, ...}
> 
> My ideas:
> Transpose -> MapAt/Map -> Transpose
> Build the sublist with Part and then rebuild it
> Use Map and a function like #[[All, 2]] and then rebuild it.
> 
> I don't like any solution. I wanted to know if there's anything simple
> that I'm overseing
> 
> Thanks guys
> 

If all pairs are of the form {name, integer} I would propose
data/.{something_, i_Integer}:>{something, i/2}
Peter


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