Interpolation Using the Previous Value
Description
These functions provide an interpolation mechanism for objects of
class lgtdl
. The AsIs
method is the vectorized version.
Usage
1 2 3 4 5  interpprev(x, ...)
## S3 method for class 'lgtdl'
interpprev(x, time, cov, ...)
## S3 method for class 'AsIs'
interpprev(x, ...)

Arguments
x 

time 
A vector of times at which interpolation is requested. 
cov 
The name of the covariate on which interpolation is
requested. It is only required if 
... 
Ignored. 
Details
If objects of class lgtdl
are inserted into a data frame they
become a vector with class AsIs
. In order to operate on these
we provide a method for that class. The method is simply a vectorized
version.
Value
interpprev.lgtdl
returns a numeric vector of the interpolated
values of the covariate at the time(s) specified by time
.
interpprev.AsIs
returns a vector of interpolated values of the
covariate. In this case the vector contains one value for each element
x
. time
must be either the same length as x
or
of length one. In the latter case all interpolations are done at that
time.
Author(s)
Robert Gentleman
See Also
interplinear
Examples
1 2 3 4 5 6  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, c(2,4))
interpprev(x2, c(12, 14))

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