R Under development (unstable) (2024-01-28 r85838 ucrt) -- "Unsuffered Consequences"
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> library(Greg)
Loading required package: Gmisc
Loading required package: Rcpp
Loading required package: htmlTable
Loading required package: forestplot
Loading required package: grid
Loading required package: checkmate
Loading required package: abind
> library(dplyr)

Attaching package: 'dplyr'

The following objects are masked from 'package:stats':

    filter, lag

The following objects are masked from 'package:base':

    intersect, setdiff, setequal, union

> data("melanoma", package = "boot")
> melanoma <- mutate(melanoma,
+                    status = factor(status,
+                                    levels = 1:3,
+                                    labels = c("melanoma-specific death", "alive", "other death")),
+                    ulcer = factor(ulcer,
+                                   levels = 0:1,
+                                   labels = c("Absent", "Present")),
+                    time = time / 365.25)
> 
> library(survival)
> regular_model <- coxph(Surv(time, status == "melanoma-specific death") ~
+                          age + sex + year + thickness + ulcer,
+                        data = melanoma,
+                        x = TRUE, y = TRUE)
> 
> spl_melanoma <- timeSplitter(melanoma,
+                              by = .1,
+                              event_var = "status",
+                              event_start_status = "alive",
+                              time_var = "time",
+                              time_related_vars = c("age", "year"))
> 
> interval_model <- update(regular_model,
+                          Surv(Start_time, Stop_time, status == "melanoma-specific death") ~ .,
+                          data = spl_melanoma)
> 
> mismatch <- abs(sum(coef(interval_model) - coef(regular_model)))
> if (mismatch > 10^-10) {
+   stop("Failed to match interval with regular cox model.",
+        " Total coefficient difference = ", mismatch,
+        "\n Regular: ", paste(txtRound(coef(regular_model), 3),
+                              collapse = ", "
+        ),
+        "\n Interval: ", paste(txtRound(coef(interval_model), 3),
+                               collapse = ", "
+        )
+   )
+ }
> 
> proc.time()
   user  system elapsed 
   3.95    0.98    4.87