Implement $has_nulls()

NEWS.md

@@ -2,6 +2,10 @@
 
 ## Polars R Package (development version)
 
+### New features
+
+- New method `$has_nulls()` (#1133).
+
 ## Polars R Package 0.17.0
 
 ### Breaking changes

R/expr__expr.R

@@ -3742,3 +3742,19 @@ Expr_qcut = function(
       unwrap("in $qcut():")
   }
 }
+
+#' Check whether the expression contains one or more null values
+#'
+#' @return Expr
+#'
+#' @examples
+#' df = pl$DataFrame(
+#'   a = c(NA, 1, NA),
+#'   b = c(1, NA, 2),
+#'   c = c(1, 2, 3)
+#' )
+#'
+#' df$select(pl$all()$has_nulls())
+Expr_has_nulls = function() {
+  self$null_count() > 0
+}

R/expr__name.R

@@ -50,7 +50,6 @@ ExprName_keep = function() {
 }
 
 # TODO: this method is broken after <https://github.com/pola-rs/r-polars/pull/1104>, so not documented
-#' @noRd
 #' Map alias of expression with an R function
 #'
 #' Rename the output of an expression by mapping a function over the root name.
@@ -69,6 +68,7 @@ ExprName_keep = function() {
 #' df$select(
 #'   pl$col("var1")$alias("foobar")$name$map(\(x) paste0("new_", x))
 #' )
+#' @noRd
 ExprName_map = function(fun) {
   if (
     !polars_options()$no_messages &&