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Last data update: 2014.03.03

R: A function to provide estimates of the response for a...

interplinear

R Documentation

A function to provide estimates of the response for a longitudinal data object. The estimate is obtained by linear interpolation from the preceding and following observations.

Description

A linear interpolation, using approx, is used to obtain estimates of the covariate at times other than those observed.

Usage

interplinear(x, ...)
## S3 method for class 'lgtdl'
interplinear(x, time, cov = NULL, ...)
## S3 method for class 'AsIs'
interplinear(x, ...)

Arguments

`x`	The `lgtdl` object that is to be interpolated.
`time`	The time(s) at which interpolation is desired.
`cov`	The name of the covariate in the `lgtdl` object on which the interpolation should be based. It is not required if there is only one covariate.
`...`	Ignored.

Value

A vector containing the interpolated estimates of the covariate values at the requested times.

Author(s)

Robert Gentleman

Examples

  x1<-data.frame(time=c(1,3,5), cov=c(4,6,8))
  x2<-data.frame(time=c(11,13,15), interest=c(66,45,88))
  x1<-as.lgtdl(x1)
  x2<-as.lgtdl(x2)
  interpprev(x1, 4)
  interpprev(x2, c(12, 14))