[R] What's the best way to tell a function about relevant fields in data frames

[Gabor Grothendieck]

You could define a generic detect(obj, ...) that dispatches (using S3):

detect.formula(fo, data)
detect.data.frame(data)
detect.default(x, y, trial)

where the first two call the third thereby modeling it on lm,
a common approach, and giving the user choice in interface.

On Tue, May 12, 2009 at 6:18 AM, Titus von der Malsburg
<malsburg at gmail.com> wrote:
>
> Hi list,
>
> I have a function that detects saccadic eye movements in a time series
> of eye positions sampled at a rate of 250Hz.  This function needs
> three vectors: x-coordinate, y-coordinate, trial-id.  This information
> is usually contained in a data frame that also has some other fields.
> The names of the fields are not standardized.
>
>> head(eyemovements)
>        time     x      y trial
> 51 880446504 53.18 375.73     1
> 52 880450686 53.20 375.79     1
> 53 880454885 53.35 376.14     1
> 54 880459060 53.92 376.39     1
> 55 880463239 54.14 376.52     1
> 56 880467426 54.46 376.74     1
>
> There are now several possibilities for the signature of the function:
>
> 1. Passing the columns separately:
>
>    detect(eyemovements$x, eyemovements$y, eyemovements$trial)
>
>  or:
>
>    with(eyemovements,
>         detect(x, y, trial))
>
> 2. Passing the data frame plus the names of the fields:
>
>    detect(eyemovements, "x", "y", "trial")
>
> 3. Passing the data frame plus a formula specifying the relevant
> fields:
>
>    detect(eyemovements, ~x+y|trial)
>
> 4. Passing a formula and getting the data from the environment:
>
>    with(eyemovements,
>         detect(~x+y|trial))
>
> I saw instances of all those variants (and others) in the wild.
>
> Is there a canonical way to tell a function which fields in a data
> frame are relevant?  What other alternatives are possible?  What are
> the pros and cons of the alternatives?
>
> Thanks, Titus
>
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>