Helper function to add strata as an attribute to a Surv object. The output of this function can be used as the response in glmnet() for fitting stratified Cox models.

stratifySurv(y, strata = rep(1, length(y)))



A Surv object.


A vector of length equal to the number of observations in y, indicating strata membership. Default is all belong to same strata.


An object of class stratifySurv (in addition to all the classes y belonged to).


When fitting a stratified Cox model with glmnet(), strata should be added to a Surv response with this helper function. Note that it is not sufficient to add strata as an attribute to the Surv response manually: if the result does not have class stratifySurv, subsetting of the response will not work properly.


y <- survival::Surv(1:10, rep(0:1, length.out = 10))
strata <- rep(1:3, length.out = 10)
y2 <- stratifySurv(y, strata)  # returns stratifySurv object