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