Mathematica 9 is now available
Services & Resources / Wolfram Forums
-----
 /
MathGroup Archive
2006
*January
*February
*March
*April
*May
*June
*July
*August
*September
*October
*November
*December
*Archive Index
*Ask about this page
*Print this page
*Give us feedback
*Sign up for the Wolfram Insider

MathGroup Archive 2006

[Date Index] [Thread Index] [Author Index]

Search the Archive

Re: Question on Thread

  • To: mathgroup at smc.vnet.net
  • Subject: [mg64459] Re: [mg64418] Question on Thread
  • From: Andrzej Kozlowski <akoz at mimuw.edu.pl>
  • Date: Fri, 17 Feb 2006 04:12:59 -0500 (EST)
  • References: <200602160805.DAA29888@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

On 16 Feb 2006, at 09:05, Matt wrote:

> Hello,
>
> Clear[f]
> Thread[(f[#1, #2] & )[{1, 2, 3}, {{a, 1}, {b, 2}, {c, 3}}]]
>
> Gives the expected output, i.e. {f[1,{a,1}], f[2,{b,2}],...}
>
> but
>
> Clear[f, g]
> Thread[(f[g[#1], #2] & )[{1, 2, 3}, {{a, 1}, {b, 2}, {c, 3}}]]
>
> gives me:
>
> f[g[{1, 2, 3}], {a, 1}], f[g[{1, 2, 3}], {b, 2}], ..., etc.
>
> whereas I would have expected:
>
> f[g[1], {a, 1}], f[g[2], {b, 2}], ..., etc.
>
> I've looked at the 'Thread' documentation and in the Mathematica Book,
> but I can't see why the second case doesn't work.
>
> BTW, I used MapThread as follows, which does work:
>
> MapThread[f[g[#1], #2] & , {{1, 2, 3}, {{a, 1}, {b, 2}, {c, 3}}}
>
> Thanks for your time,
>
> Matt
>


The reason is that Thread evaluates its arguments. Use

In[7]:=
Thread[Unevaluated[(f[g[#1], #2] & )[{1, 2, 3}, {{a, 1}, {b, 2}, {c,  
3}}]]]

Out[7]=
{f(g(1),{a,1}),f(g(2),{b,2}),f(g(3),{c,3})}

Andrzej Kozlowski



  • Prev by Date: Re: Using a text editor like interface for Mathematica?
  • Next by Date: Re: Mathematica:recursion with 2 arguments?
  • Previous by thread: Question on Thread
  • Next by thread: Re: Question on Thread