R: Extract time band data from a split Lexis object

timeBand {Epi} | R Documentation

## Extract time band data from a split Lexis object

### Description

The break points of a `Lexis` object (created by a call to `splitLexis`) divide the follow-up intervals into time bands along a given time scale. The `breaks` function returns the break points, for a given time scale, and the `timeBand` classifies each row (=follow-up interval) into one of the time bands.

### Usage

    timeBand(lex, time.scale, type="integer")
    breaks(lex, time.scale)

### Arguments

`lex` | an object of class `Lexis`
`time.scale` | a character or integer vector of length 1 identifying the time scale of interest
`type` | a string that determines how the time bands are labelled. See Details below

### Details

Time bands may be labelled in various ways according to the `type` argument. The permitted values of the `type` argument, and the corresponding return values are:

"integer"

  a numeric vector with integer codes starting from 0.

"factor"

  a factor (unordered) with labels "(left,right]"

"left"

  the left-hand limit of the time band

"middle"

  the midpoint of the time band

"right"

  the right-hand limit of the time band

### Value

The `breaks` function returns a vector of break points for the `Lexis` object, or NULL if no break points have been defined by a call to `splitLexis`. The `timeBand` function returns a numeric vector or factor, depending on the value of the `type` argument.

### Note

A newly created `Lexis` object has no break points defined. In this case, `breaks` will return NULL, and `timeBand` will a vector of zeros.

### Author(s)

Martyn Plummer

### See Also

`Lexis`

### Examples

    data(diet)
    diet <- cal.yr(diet)
    diet.lex <- Lexis(entry=list(period=doe),
                       exit=list(period=dox, age=dox-dob),
                exit.status=chd,
                       data=diet)
    diet.split <- splitLexis(diet.lex, breaks=seq(40,70,5), "age" )
    age.left <- timeBand(diet.split, "age", "left")
    table(age.left)
    age.fact <- timeBand(diet.split, "age", "factor")
    table(age.fact)
    age.mid <- timeBand(diet.split, "age", "mid")
    table(age.mid)

[Package Epi version 2.44 Index]