Helper function for Cox deviance and gradient

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.

Examples

# Example with no ties
glmnet:::fid(c(1, 4, 5, 6), 1:5)
#> $index_first
#> [1] 1 2 3 4 5
#> 
#> $index_ties
#> NULL
#> 

# Example with ties
glmnet:::fid(c(1, 1, 1, 2, 3, 3, 4, 4, 4), 1:9)
#> $index_first
#> [1] 1 4 5 7
#> 
#> $index_ties
#> $index_ties$`1`
#> [1] 1 2 3
#> 
#> $index_ties$`3`
#> [1] 5 6
#> 
#> $index_ties$`4`
#> [1] 7 8 9
#> 
#>