Handling options in my function [duplicate]

Question

It seems this should be easy, by I just can not figure out how. I'm making many very similar style plots, so I want to make a function with all the default options specified. Sometimes I need to tweak a plot though, like changing a color or adding a legend, so I want to be able to pass options to it if I want. If a want to tweak the plot the following function works

fplot[f_, range_, opt_] := 
  Plot[f, range, PlotLabel -> "A plot", Frame -> True, Axes -> False, opt];

fplot[Sin[x], {x, 0, 2 \[Pi]}, {PlotStyle -> Orange,    
  FrameLabel -> {{"y[x]", ""}, {"x", ""}}}]

But I also want my function to be able to handle me not giving it options, so I want the following to work as well

fplot[Sin[x], {x, 0, 2 \[Pi]}]

which now just gives me back the output:fplot[Sin[x], {x, 0, 2 [Pi]}]

I have loot at similar questions of passing optional options to a function, but I can't get either method to work, and they seem the require that I predefine the Options that I might later want to tweak. I would like to be able to tweak any of the options in Plot without having to predefine them. Passing list of options to Plot

Pass list of options to Plot3D

Any help is much apprechiated!

Answer 1

When you evaluate the statement opt=="def" it evaluates to True if opt really is "def", but it doesn't give False for any other object.

Read the answer here to see why you need to use SameQ (===) instead of Equal (==),

f[a_, opt_] := Module[{defOpt, opt2},
  defOpt = {PlotLabel -> "Label"};
  If[opt === "def", opt2 = defOpt, opt2 = Join[defOpt, opt]];
  Plot[Sin[a x], {x, 0, 2 π}, Evaluate@opt2]]

For the record, the easiest way to define the function you have there is

f[a_, opt : OptionsPattern[Plot]] :=
  Plot[Sin[a x], {x, 0, 2 π}, opt, PlotLabel -> "Label"]

and then

f[2]
f[2, Background -> LightBlue, PlotStyle -> Orange]

would give the exact same output as above

Answer 2

To define a function with options, give it a set of defaults and use OptionsPattern in the definition. To use the value of a particular option in the function defintion, use OptionValue:

Options[f] = {"ThisIsAnOption" -> False, SoIsThis -> 1};

f[a_, opt : OptionsPattern[]] :=
 (If[OptionValue["ThisIsAnOption"], Print[{opt}]]; a + OptionValue[SoIsThis])

If f is used without specifying any options, OptionValue will use the default values:

f[2]

(* 3 *)

If you specify an option where OptionsPattern[] is used in the definition, you can override the default values:

f[2, "ThisIsAnOption" -> True]

(* {"ThisIsAnOption"->True} *)
(* 3 *)

You can just add more options as you like and the order of the option arguments doesn't matter, so long as they all occur in sequence where OptionsPattern[] was specified:

f[2, SoIsThis -> 2, "ThisIsAnOption" -> True]

(* {SoIsThis->2, "ThisIsAnOption"->True} *)
(* 4 *)

This will trigger a message because "NotValidOption was never given for Options[f]:

f[2, "NotValidOption" -> "hello"]

(* OptionValue::nodef: Unknown option NotValidOption for f. *)
(* 3 *)

For your specific example, you can set the options of f to have the same options as Plot and override the default for PlotLabel with SetOptions. Then it's just a matter of passing the options argument to Plot. Here I used Join because it will take the first option value it finds if there are any duplicates:

Options[f] = Options[Plot];
SetOptions[f, PlotLabel -> "Label"];

f[a_, opts : OptionsPattern[]] := 
    Plot[Sin[a x], {x, 0, 2 Pi}, Evaluate[Join[{opts}, Options[f]]]];