R: Formula based version of lapply.

by-lapply {doBy}

R Documentation

Formula based version of lapply.

Description

This function is a wrapper for calling lapply on the list resulting from first calling splitBy.

Usage

lapplyBy(formula, data = parent.frame(), FUN)

Arguments

`formula`	A formula describing how data should be split.
`data`	A dataframe.
`FUN`	A function to be applied to each element in the splitted list, see 'Examples' below.

Value

A list.

Author(s)

Søren Højsgaard, sorenh@math.aau.dk

Examples

data(dietox)

## Calculate weekwise feed efficiency = weight gain / feed intake
dietox <- orderBy(~Pig + Time, data=dietox)
v <- lapplyBy(~Pig, data=dietox,
              function(d) c(NA, diff(d$Weight) / diff(d$Feed)))
dietox$FE <- unlist(v)

## Technically this is the same as 
dietox <- orderBy(~Pig + Time, data=dietox)
wdata <- splitBy(~Pig, data=dietox)
v <- lapply(wdata, function(d) c(NA, diff(d$Weight)/diff(d$Feed)))
dietox$FE <- unlist(v)

[Package doBy version 4.6-2 Index]