# Find the Most Recent Value of a Time-varying Covariate Before Each Observed Response

### Description

`gettvc`

finds the most recent value of a time-varying covariate
before each observed response and possibly adds them to a list of other
time-varying covariates.
It compares the times of response observations with those of
time-varying covariates to find the most recent observed time-varying
covariate for each response. These are either placed in a new object of
class, `tvcov`

, added to an already existing list of matrices containing
other time-varying covariates and a new object of class, `tvcov`

,
created, or added to an existing object of class, `tvcov`

.

If there are response observation times before the first covariate time, the covariate for these times is set to zero.

### Usage

1 2 |

### Arguments

`response` |
A list of two column matrices with response values and
times for each individual, one matrix or dataframe of response
values, or an object of class, |

`times` |
When |

`tvcov` |
A list of two column matrices with time-varying covariate values and corresponding times for each individual or one matrix or dataframe of such covariate values. Times need not be the same as for responses. |

`tvctimes` |
When the time-varying covariate is a matrix, a vector of possibly unequally spaced times for the covariate, when they are the same for all individuals or a matrix of times. Not necessary if equally spaced. |

`oldtvcov` |
A list of matrices with time-varying covariate values,
observed at the event times in |

`ties` |
If TRUE, when the response and covariate times are identical, the response depends on that new value (as in observational studies); if FALSE, only the next response depends on that value (for example, if the covariate is a new treatment just applied at that time). |

### Value

An object of class, `tvcov`

, is returned containing the new time-varying
covariate and, possibly, those in `oldtvcov`

.

### Author(s)

J.K. Lindsey and D.F. Heitjan

### See Also

`read.list`

, `restovec`

,
`tvctomat`

.

### Examples

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 | ```
## Not run:
y <- matrix(rnorm(20), ncol=5)
resp <- restovec(y, times=c(1,3,6,10,15))
z <- matrix(rpois(20,5),ncol=5)
z
# create a new time-varying covariate object for the response
newtvc <- gettvc(resp, tvcov=z, tvctimes=c(1,2,5,12,14))
covariates(newtvc)
# add another time-varying covariate to the object
z2 <- matrix(rpois(20,5),ncol=5)
z2
newtvc2 <- gettvc(resp, tvcov=z2, tvctimes=c(0,4,5,12,16), oldtvc=newtvc)
covariates(newtvc2)
## End(Not run)
``` |