Re: Listable functions with two brackets f[][] (SubValues)
- To: mathgroup at smc.vnet.net
- Subject: [mg64944] Re: Listable functions with two brackets f[][] (SubValues)
- From: Peter Pein <petsie at dordos.net>
- Date: Wed, 8 Mar 2006 01:00:25 -0500 (EST)
- References: <dujrti$923$1@smc.vnet.net>
- Sender: owner-wri-mathgroup at wolfram.com
Goyder Dr HGD schrieb:
> I would like to use a double bracket function f[][] as, I believe,
> originally promoted by David Park. The second bracket is called the
> SubValues of f. My problem is that I would like the second bracket to
> be Listable. Is this possible.?
>
> The following is a toy example by way of illustration. Suppose I wish
> to make a function that translates the graphics primitive Line. Then I
> can make a function as follows and it works for one Line[].
>
> In[1]:=
> ClearAll[f];
> f[vec_][a_Line] := Line[(#1 + vec & ) /@ a[[1]]]
>
> In[3]:=
> b = Line[{{1, 2}, {3, 4}, {5, 6}}];
>
> In[4]:=
> f[{1, 3}][b]
>
> Out[4]=
> Line[{{2,5},{4,7},{6,9}}]
>
> However, if I have a list of Lines[] it does not work because the
> second bracket does not have the Attribute Listable.
>
> In[5]:=
> c = {b, Line[{{2, 3}, {5, 6}, {9, 3}}]};
>
> In[6]:=
> f[{1, 3}][c]
>
> Out[6]=
> f[{1,3}][{Line[{{1,2},{3,4},{5,6}}],Line[{{2,3},{5,6},{9,3}}]}]
>
> Attempts to make the function f[][] Listable fail because it makes the
> first and not the second bracket Listable.
>
> In[7]:=
> SetAttributes[f, Listable]
>
> In[8]:=
> f[{1, 3}][c]
>
> Out[8]=
> {f[1],f[3]}[{Line[{{1,2},{3,4},{5,6}}],Line[{{2,3},{5,6},{9,3}}]}]
>
> Is there a solution?
>
> Thanks
> Hugh Goyder
>
Hello Hugh,
is
f[{1, 3}] /@ c
--> {Line[{{2, 5}, {4, 7}, {6, 9}}], Line[{{3, 6}, {6, 9}, {10, 6}}]}
an option?