fid: Helper function for Cox deviance and gradient

Description

Helps to find ties in death times of data.

Usage

fid(x, index)

Arguments

x

Sorted vector of death times.

index

Vector of indices for the death times.

Value

A list with two arguments.

index_first

A vector of indices for the first observation at each
death time as they appear in the sorted list.

index_ties

If there are no ties at all, this is NULL. If not, this is
a list with length equal to the number of unique times with ties. For each
time with ties, index_ties gives the indices of the observations with a
death at that time.