Control the length of the output of the variance function

[martinchevalier]

At least in simple cases, the output of the variance function should be of length the number of columns of the Y variable in input.

• Determine whether this has to be true in all cases
• If so, try to test it at the variance definition step (it may need a dry-run of the variance function) or at the execution step (easier)

MWE (thanks to @ThomasDeroyon) :

data <- data.frame(id = 1:100, sex= c(rep(1, 50), rep(2, 50)), 
                   y = c(rnorm(50, 1, 3), rnorm(50, 2, 4)), weight = rep(10, 100))

# Dont't work
variance_function <- function(y) 1
variance_wrapper <- gustave::define_variance_wrapper(variance_function = variance_function,
                                                     reference_id = data$id, 
                                                     reference_weight = data$weight, 
                                                     default_id = "id")
variance_wrapper(data, as.factor(sex))

# Works
variance_function <- function(y) rep(1, NCOL(y))
variance_wrapper <- gustave::define_variance_wrapper(variance_function = variance_function,
                                                     reference_id = data$id, 
                                                     reference_weight = data$weight, 
                                                     default_id = "id")
variance_wrapper(data, as.factor(sex))