interplinear {lgtdl}

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

See Also

interpprev

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))