Mathematica 9 is now available
Services & Resources / Wolfram Forums
-----
 /
MathGroup Archive
1995
*January
*February
*March
*April
*May
*June
*July
*August
*September
*October
*November
*December
*Archive Index
*Ask about this page
*Print this page
*Give us feedback
*Sign up for the Wolfram Insider

MathGroup Archive 1995

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

Search the Archive

Options and FilterOptions

  • To: mathgroup at christensen.cybernetics.net
  • Subject: [mg946] Options and FilterOptions
  • From: Allan Hayes <hay%haystack at christensen.cybernetics.net>
  • Date: Wed, 3 May 1995 00:25:30 -0400

Here are some general points about options and the function  
FilterOptions that might be of use.

1) Options can be of the form name:> value as well as name->value .
So, one should normally use the form
	foo[___, opts___?OptionQ]

2) Nested list of options are accepted by OptionQ

In[1]:=
	OptionQ[{a->b,{{x :> y}}}]
Out[1]=
	True

and by other functions: eg

In[2]:=
	Plot[x,{x,0,1}, {Frame ->True}];

They can appear, or be generated, in code (though with care we  
could probably avoid this).

Unfortunately we find

2a) A problem with ReplaceAll

In[3]:=
	{a,x}/.{a->b,{{x :> y}}}
	ReplaceAll::rmix:
   	Elements of {a -> b, {{x :> y}}} are a mixture of lists and	 
non-lists.
Out[3]=
	{a, x} /. {a -> b, {{x :> y}}}

Solution: use

	expr/.Flatten[{opts}]/.Options[foo]
	
(We don't need to use Flatten[Options[symbol]]] since even if 	
 we define
 In[4]:=
	Options[foo] = {{a->b},{{c->d}}};
 Which is probably undesirable, we still get
 In[5]:=
	Options[foo]
 Out[5]=
	{a -> b, c -> d}
)

2b) A problem with FilterOptions and lists of options.

In[6]:=
	Needs["Utilities`FilterOptions`"]
In[8]:=
	FilterOptions[Plot, {PlotPoints -> 10,Frame->True}]
	
	Function::fpct:
   	Too many parameters in {FE`e} to be filled from
    	Function[{FE`e}, LinkWrite[$ParentLink, <<1>>], {HoldAll}][].
Out[7]=
	Sequence[]

This is not what we wanted; which was
	Sequence[PlotPoints -> 10, Frame -> True]

Solution: use
	
	FilterOptions[symbol, Sequence@@Flatten[{opts}]]

In[8]:=
	FilterOptions[Plot,
	 Sequence@@Flatten[{{PlotPoints -> 10,Frame->True}}]]
Out[8]=
	Sequence[PlotPoints -> 10, Frame -> True]

Or we could temporarily define
In[9]:=
	FilterOptions2[foo_Symbol,opts___?OptionQ]:=
		FilterOptions[foo, Sequence@@Flatten[{opts}] ]

Of course, this trick could be built into a new version of FilterOptions.

Finally: Messages are generated in the next two examples but they  
can be ignored as the answers are correct

  In[11]:=
	FilterOptions[Plot, Sequence@@Flatten[{a->b}]]
	Function::fpct:
   	Too many parameters in {FE`e} to be filled from
    	Function[{FE`e}, <<1>>, {HoldAll}][].
  Out[10]=
	Sequence[]
  In[12]:=
	FilterOptions[Plot, Sequence@@Flatten[{}]]
	Function::fpct:
   	Too many parameters in {FE`e} to be filled from
    	Function[{FE`e}, <<1>>, {HoldAll}][].
  Out[11]=
	Sequence[]
  These messages are caused by the attempted evaluation of Sequence[] 	
  (which is returned unevaluated):
  In[13]:=
	Sequence[]
	Function::fpct:
   	Too many parameters in {FE`e} to be filled from
    	Function[{FE`e}, <<1>>, {HoldAll}][].
   Out[12]=
	Sequence[]

Allan Hayes
hay at haystack.demon.uk


  • Prev by Date: Re: Programming: List Structure Manipulation
  • Next by Date: Re: Kernel configuration for DEC Alpha on VMS
  • Previous by thread: Re: Programming: List Structure Manipulation
  • Next by thread: Re: Options and FilterOptions