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.