In two words, use -gettoken-.
First off, the -syntax- statement for -by()- is better as
BY(str asis)
The following code should help:
if `"`by'"' != "" {
gettoken by opts : by, parse(",")
gettoken comma opts : opts, parse(",")
local byby `"by(`by', `opts')"'
}
Your byvariable is now in local macro by
and you can pass local macro byby to -twoway graph-.
You will probably need to add some flourishes
to this to get the behaviour you want.
Other details can be seen by looking inside user-written
graphics programs that provide -by()- support.
Nick
[email protected]
Eva Poen
> I am in the process of writing a small graphics command. It is
> supposed to produce a bar chart like
>
> -graph bar (mean) price, over(rep78) by(foreign)-
>
> but with the number of observations (or percentages) represented by
> each bar added to the graph. The program is based on some code
> suggested by Nick Cox to one of my colleagues.
>
> So far, my syntax statement reads:
>
> syntax varlist(min=2 max=2) [if] [in] [, BY(varname) *]
>
> I added the * to the options list to capture any general graphics
> options the user might give. But I need to explicitly state the by()
> option (instead of leaving it to *), because I need the by-Variable in
> some of the calculations before creating the graph.
>
> The problem comes with the nested suboptions for -graph, twoway-. If
> the user specifies the by() option in my program, some of the general
> graphics options need to go inside by() for the final graph (e.g.
> legend(position()), title()) while others go outside by(), like
> xlabel(), xtitle(), legend(col()).
>
> How can I best implement this in my program? I thought about adding
> another option called byoption to capture everything that needs to go
> inside by(), but it seems rather inelegant. Or is there an easy way to
> scan the general options list created by * for the existence of by()
> and extract just the variable name, for use in my calculations?
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