by is an object-oriented wrapper for
tapply applied to data frames.
an R object, normally a data frame, possibly a matrix.
a factor or a list of factors, each of length
a function to be applied to (usually data-frame) subsets of
further arguments to
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.
For the default method, an object with dimensions (e.g., a matrix) is
coerced to a data frame and the data frame method applied. Other
objects are also coerced to a data frame, but
FUN is applied
separately to (subsets of) each column of the data frame.
An object of class
"by", giving the results for each subset.
This is always a list if
simplify is false, otherwise a list or
ave also applies a function block-wise.
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require(stats) by(warpbreaks[, 1:2], warpbreaks[,"tension"], summary) by(warpbreaks[, 1], warpbreaks[, -1], summary) by(warpbreaks, warpbreaks[,"tension"], function(x) lm(breaks ~ wool, data = x)) ## now suppose we want to extract the coefficients by group tmp <- with(warpbreaks, by(warpbreaks, tension, function(x) lm(breaks ~ wool, data = x))) sapply(tmp, coef)
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