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MathGroup Archive 2006

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Re: RandomList and pure function

  • To: mathgroup at smc.vnet.net
  • Subject: [mg70887] Re: RandomList and pure function
  • From: albert <awnl at arcor.de>
  • Date: Mon, 30 Oct 2006 05:33:33 -0500 (EST)
  • References: <ei18or$8n7$1@smc.vnet.net>

Marc VIAL wrote:

> 
> Hi,
> 
> Sorry for this naive question, but I try to apply a pure function of 2
> arguments to a list of n rows with 2 clm using the mapping function:
> 
> n=100;lis=RandomReal[{0,1},{n,2}];
> (#1+2 #2)&/@lis
> 
> however it only captures the first term in the list and leave #2
> unassigned.
> 
> Any advice?

Note that using your construct the pure function does not see two arguments
but one argument which happens to be a list of two numbers. So this should
work:

(#[[1]]+2*#[[2]])& /@ lis

If you want to apply a function of two arguments, you will in this case need
to use Apply, not Map. The following does this:

(#1 + 2 #2) & @@@ lis

and is a shorthand for:

Apply[(#1 + 2 #2) &, lis, {1}]

hth,

albert


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