by-transform: 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.