Extract time band data from a split Lexis object

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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

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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

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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)

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