Re: Listable functions with two brackets f[][] (SubValues)

*To*: mathgroup at smc.vnet.net*Subject*: [mg64950] Re: Listable functions with two brackets f[][] (SubValues)*From*: Paul Abbott <paul at physics.uwa.edu.au>*Date*: Wed, 8 Mar 2006 01:00:57 -0500 (EST)*Organization*: The University of Western Australia*References*: <dujrti$923$1@smc.vnet.net>*Sender*: owner-wri-mathgroup at wolfram.com

In article <dujrti$923$1 at smc.vnet.net>, "Goyder Dr HGD" <h.g.d.goyder at cranfield.ac.uk> wrote: > 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.? AFAIK, not using the Listable Attribute -- but you can easily get the behaviour you want. > 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]]] Alternatively, you could write f[vec_][Line[a_]] := Line[(# + vec &) /@ a] > 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}}]}] Just add the rule f[vec_][a_List] := f[vec] /@ a and then try f[{1, 3}][c] again. > 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? Not using Listable, I think. Cheers, Paul _______________________________________________________________________ Paul Abbott Phone: 61 8 6488 2734 School of Physics, M013 Fax: +61 8 6488 1014 The University of Western Australia (CRICOS Provider No 00126G) AUSTRALIA http://physics.uwa.edu.au/~paul