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Re: Distinquishing #'s in nested pure functions

  • To: mathgroup at smc.vnet.net
  • Subject: [mg126283] Re: Distinquishing #'s in nested pure functions
  • From: Murray Eisenberg <murray at math.umass.edu>
  • Date: Sat, 28 Apr 2012 05:29:38 -0400 (EDT)
  • Delivered-to: l-mathgroup@mail-archive0.wolfram.com
  • References: <201204260933.FAA05752@smc.vnet.net> <201204271048.GAA20037@smc.vnet.net>
  • Reply-to: murray at math.umass.edu

The symbol # is an abbreviation for #1. You can have #1, #2, etc.

And actually, #1, #2, etc., are in turn abbreviations for the FullForm 
names Slot[1], Slot[2], etc.

On 4/27/12 6:48 AM, Dave Snead wrote:
> Hi,
>
> Is there a way to distinguish the #'s in nested pure functions?
>
> As a simple example:
>
> f[x_, y_] := x - y
>
> Select[{1, 2, 3}, (f[#, #]&  /@ {-1, -2, -3}) == {3, 4, 5}&]
>
> I want the 1st # to correspond with the outer&  (the equal)
> and the 2nd # with the inner&  (the map)
> The answer in this example should by {2}
> (of course, the statement as written above does not do the job)
>
> Can Mathematica distinguish these #'s?
>
> Thanks in advance,
> Dave Snead
>
>

-- 
Murray Eisenberg                     murray at math.umass.edu
Mathematics & Statistics Dept.
Lederle Graduate Research Tower      phone 413 549-1020 (H)
University of Massachusetts                413 545-2859 (W)
710 North Pleasant Street            fax   413 545-1801
Amherst, MA 01003-9305



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