Re: tricky question
- To: mathgroup at smc.vnet.net
- Subject: [mg27965] Re: [mg27960] tricky question
- From: BobHanlon at aol.com
- Date: Tue, 27 Mar 2001 01:26:03 -0500 (EST)
- Sender: owner-wri-mathgroup at wolfram.com
Clear[g];
g[x_,y_] := Map[ Times[ x, # ]&, y ];
ans = g[x, {y1, y2, y3}]
{x*y1, x*y2, x*y3}
As a pure function
Clear[g];
g := Thread[Times[#1, #2]]&
g[x, {y1, y2, y3}] == ans
True
However, since Times is Listable this simplifys to
Clear[g];
g := #1*#2&;
g[x, {y1, y2, y3}] == ans
True
Bob Hanlon
In a message dated 2001/3/26 5:56:44 AM, linsuain+ at andrew.cmu.edu writes:
>this question has been teasing my brain for a while. It is about the
>apparent IMPOSSIBILITY of defining certain functions as pure functions.
>
>first take a simple case where it is POSSIBLE to define a pure function:
>
>g[x_,y_]:= Times[x,y] will do the same as g := Times[ #1, #2 ] &
>
>now in this case it seems to me it is IMPOSSIBLE to define a pure function:
>
>g[x_,y_] := Map[ Times[ x, # ]&, y ]
>
>is NOT the same as g := Map[ Times[ #1, #]& , #2]&
>
>the reason these two are not the same is that in the function on the top
>line the arguments of Times would be x and the parts of y at level 1
>taken in sequence, while in the function on the botton line, the
>arguments of Times would both be just x, since #1 and # stand for the
>same.
>
>So, the question is: can g[x_,y_] := Map[ Times[ x, # ]&, y ] be input
>as a pure function?
>