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MathGroup Archive 2006

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Re: Mapping Functions That Take More Than One Argument

  • To: mathgroup at smc.vnet.net
  • Subject: [mg69897] Re: [mg69864] Mapping Functions That Take More Than One Argument
  • From: Gregory Lypny <gregory.lypny at videotron.ca>
  • Date: Wed, 27 Sep 2006 06:03:54 -0400 (EDT)
  • References: <NDBBJGNHKLMPLILOIPPOOEOAFCAA.djmp@earthlink.net>

Excellent.  Thank you, David.  My collection of MathGroup tips is  
growing and growing.

	Gregory

On Tue, Sep 26, 2006, at 10:03 AM, David Park wrote:

> Gregory,
>
> To map a function with more than one argument over a list, use a pure
> function with the other arguments filled in.
>
> testlist = {{1, 2, 3}, {4, 5, 6}, {7, 8, 9}};
>
> Map[Drop[#, 1] &, testlist]
> {{2, 3}, {5, 6}, {8, 9}}
>
> Or
>
> Drop[#, 1] & /@ testlist
> {{2, 3}, {5, 6}, {8, 9}}
>
> Suppose you want to map over two lists, one for each argument?  
> Suppose you
> want to drop 1 argument in the first list, 2 arguments in the  
> second list,
> and the last argument in the third list. Do it with a pure function  
> and
> MapThread.
>
> MapThread[Drop[#1, #2] &, {testlist, {1, 2, -1}}]
> {{2, 3}, {6}, {7, 8}}
>
> David Park
> djmp at earthlink.net
> http://home.earthlink.net/~djmp/
>
>
>
>
>
> From: Gregory Lypny [mailto:gregory.lypny at videotron.ca]
To: mathgroup at smc.vnet.net
>
> Hello everyone,
>
> How can I map a functions onto sub-lists when the function takes more
> than one argument.  I can't seem to stumble upon the right syntax.
>
> Here's a list of three sub-lists.
>
> {{1, 2, 3}, {4, 5, 6}, {7, 8, 9}}
>
> I want to drop the first element of each sub-list, that is, 1 from
> the first, 4 from the second, and 7 from the third.
>
> Drop[{{1, 2, 3}, {4, 5, 6}, {7, 8, 9}}, 1]
>
> gives me
>
> {{4, 5, 6}, {7, 8, 9}},
>
> which is what I expected (I'm learning) but not what I want.  So, how
> do I apply Drop to each sub-list?
>
> Regards,
>
> 	Gregory
>


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