transformBy: Function to make groupwise transformations

Description

Function to make groupwise transformations of data by applying the
transform function to subsets of data.

Usage

transformBy(formula, data, ...)

Arguments

formula

A formula with only a right hand side, see examples below

data

A data frame

...

Further arguments of the form tag=value

Value

The modified value of the dataframe data.

Details

The ... arguments are tagged vector
expressions, which are evaluated in the data frame data. The tags are
matched against names(data), and for those that match, the value
replace the corresponding variable in data, and the others are appended
to data.