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Re: Redirecting input

  • To: mathgroup at smc.vnet.net
  • Subject: [mg92380] Re: Redirecting input
  • From: Szabolcs Horvat <szhorvat at gmail.com>
  • Date: Tue, 30 Sep 2008 07:34:02 -0400 (EDT)
  • Organization: University of Bergen
  • References: <200809271047.GAA22530@smc.vnet.net> <gbqcqk$e6c$1@smc.vnet.net>

Thomas Dowling wrote:
> Or, slightly simpler,
> 
> 
> f[x_] := x + 1
> 
> 
> In[7]= f@{100, 23, 44}
> 
> Out[7]= {101, 24, 45}
> 
> (rather than f /@ {100, 23, 44})
> 
> f@2, etc.

This is misleading advice.  The correct way is of course to use Map, 
i.e. f /@ {1,2,3}.  Your specific example accidentally works because 
Plus happens to have the attribute Listable, but you did not mention 
this explicitly.

With the function f[x_] := If[x > 0, x, 0],  f[{1,2,3}] (which is 
equivalent to f @ {1,2,3}) would produce a different result from f /@ 
{1,2,3}.


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