#' Sample longitudinal data for decision tree examples
#'
#' A sample balanced longitudinal dataset with 50 subjects
#' observed at 10 equally spaced time points.
#'
#' @format A data frame with 500 rows and 7 variables:
#' \describe{
#'   \item{y}{Response variable (continuous).}
#'   \item{subject}{Subject identifier (integer, 1--50).}
#'   \item{time}{Time point (integer, 1--10).}
#'   \item{x1}{Baseline covariate 1 (integer, 1--10).}
#'   \item{x2}{Baseline covariate 2 (integer, 1--10).}
#'   \item{x3}{Baseline covariate 3 (integer, 1--6).}
#'   \item{x4}{Baseline covariate 4 (integer, 1--12).}
#' }
#'
"ltreedata"
