by {base} | R Documentation |
Function by
is an object-oriented wrapper for
tapply
applied to data frames.
by(data, INDICES, FUN, ..., simplify = TRUE)
data |
an R object, normally a data frame, possibly a matrix. |
INDICES |
a factor or a list of factors, each of length
|
FUN |
a function to be applied to data frame subsets of |
... |
further arguments to |
simplify |
logical: see |
A data frame is split by row into data frames
subsetted by the values of one or more factors, and function
FUN
is applied to each subset in turn.
Object data
will be coerced to a data frame by the default
method, but if this results in a 1-column data frame, the
objects passed to FUN
are dropped to a subsets of that column.
(This was the long-term behaviour, but only documented since R 2.7.0.)
An object of class "by"
, giving the results for each subset.
This is always a list if simplify
is false, otherwise a list or
array (see tapply
).
tapply
require(stats)
attach(warpbreaks)
by(warpbreaks[, 1:2], tension, summary)
by(warpbreaks[, 1], list(wool = wool, tension = tension), summary)
by(warpbreaks, tension, function(x) lm(breaks ~ wool, data = x))
## now suppose we want to extract the coefficients by group
tmp <- by(warpbreaks, tension, function(x) lm(breaks ~ wool, data = x))
sapply(tmp, coef)
detach("warpbreaks")