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

### See Also

`lapplyBy`

### 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 4.6.5 Index]