[R] What's the best way to tell a function about relevant fields in data frames
Titus von der Malsburg
malsburg at gmail.com
Tue May 12 12:18:59 CEST 2009
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.
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)
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
4. Passing a formula and getting the data from the environment:
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?
More information about the R-help