Services & Resources / Wolfram Forums / MathGroup Archive
-----

MathGroup Archive 2007

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

Search the Archive

Re: "vector" Map[] / functional outer product?

  • To: mathgroup at smc.vnet.net
  • Subject: [mg83792] Re: "vector" Map[] / functional outer product?
  • From: Szabolcs Horvát <szhorvat at gmail.com>
  • Date: Fri, 30 Nov 2007 05:29:43 -0500 (EST)
  • References: <fim8tq$rmd$1@smc.vnet.net>

Mitch Murphy wrote:
> greetings,
> 
> is there a simpler way to express
> 
> 	{f@#,g@#}& /@ {a,b,c}
> 
> 	-> {{f[a],g[a]},{f[b],g[b]},{f[c],g[c]}}
> 
> ie. is there some mathematica function ??? such that
> 
> 	{f,g} ??? {a,b,c}
> 
> 	-> {{f[a],g[a]},{f[b],g[b]},{f[c],g[c]}}


There is no single function, but there are many ways to do it.

In[6]:= Through /@ Thread[{f, g}[{a, b, c}]]
Out[6]= {{f[a], g[a]}, {f[b], g[b]}, {f[c], g[c]}}

> 
> you might be asking what's so difficult about the "@#,@#,... & /@"  
> syntax, but what about when you don't have two functions f,g but 8-10  
> functions... the syntax gets ugly fast and hard to read.
> 
> note that
> 
> 	Outer[{f, g}, {a, b, c}]
> 
> 	-> {{f, g}[a], {f, g}[b], {f, g}[c]}


In[2]:= Outer[{f, g}, {a, b, c}]
Out[2]= {{f, g}[a], {f, g}[b], {f, g}[c]}

In[3]:= Through /@ %
Out[3]= {{f[a], g[a]}, {f[b], g[b]}, {f[c], g[c]}}

> 
> doesn't work, neither does
> 
> 	Outer[Apply, {f, g}, {a, b, c}]
> 
> 	->{{a, b, c},{a, b, c}}
> 

In[4]:= Outer[#2[#1] &, {a, b, c}, {f, g}]
Out[4]= {{f[a], g[a]}, {f[b], g[b]}, {f[c], g[c]}}

Apply[] and #1[#2] are not the same thing.

-- 
Szabolcs


  • Prev by Date: Re: "vector" Map[] / functional outer product?
  • Next by Date: Re: Reading excel data
  • Previous by thread: Re: "vector" Map[] / functional outer product?
  • Next by thread: Re: "vector" Map[] / functional outer product?