Export is_polars_dtype()

NAMESPACE

@@ -258,6 +258,7 @@ export(as_polars_df)
 export(as_polars_lf)
 export(as_polars_series)
 export(is_polars_df)
+export(is_polars_dtype)
 export(is_polars_lf)
 export(is_polars_series)
 export(pl)

NEWS.md

@@ -14,6 +14,7 @@
 - New functions `pl$datetime()`, `pl$date()`, and `pl$time()` to easily create
   Expr of class datetime, date, and time via columns and literals (#918).
 - New function `pl$arg_where()` to get the indices that match a condition (#922).
+- New function `is_polars_dtype()` (#927).
 
 ## Polars R Package 0.15.1
 

R/dataframe__frame.R

@@ -279,10 +279,10 @@ pl_DataFrame = function(..., make_names_unique = TRUE, schema = NULL) {
   # no args create empty DataFrame
   if (length(largs) == 0L) {
     if (!is.null(schema)) {
-      largs = lapply(seq_along(schema), \(x) {
+      out = lapply(seq_along(schema), \(x) {
         pl$lit(numeric(0))$cast(schema[[x]])$alias(names(schema)[x])
-      })
-      out = pl$select(largs)
+      }) |>
+        pl$select()
     } else {
       out = .pr$DataFrame$default()
     }

R/datatype.R

@@ -85,12 +85,20 @@ print.RPolarsDataType = function(x, ...) {
 "!=.RPolarsDataType" = function(e1, e2) e1$ne(e2)
 
 
-#' check if x is a valid RPolarsDataType
-#' @name is_polars_dtype
-#' @noRd
-#' @param x a candidate
-#' @return a list DataType with an inner DataType
-#' @examples .pr$env$is_polars_dtype(pl$Int64)
+#' Check if input is a valid DataType
+#'
+#' @param x An object to be tested.
+#' @param include_unknown If `FALSE` (default), `pl$Unknown` is considered as
+#' an invalid datatype.
+#'
+#' @export
+#' @return A boolean scalar.
+#'
+#' @examples
+#' is_polars_dtype(pl$Int64)
+#' is_polars_dtype(mtcars)
+#' is_polars_dtype(pl$Unknown)
+#' is_polars_dtype(pl$Unknown, include_unknown = TRUE)
 is_polars_dtype = function(x, include_unknown = FALSE) {
   inherits(x, "RPolarsDataType") && (x != pl$Unknown || include_unknown)
 }

tests/testthat/test-datatype.R

@@ -132,3 +132,12 @@ test_that("allow '*' for time_zone", {
 
   expect_identical(df$select(pl$col(pl$Datetime("ms", "*")))$width, 1)
 })
+
+test_that("is_polars_dtype works", {
+  expect_true(is_polars_dtype(pl$Int64))
+  expect_false(is_polars_dtype("numeric"))
+  expect_false(is_polars_dtype(mtcars))
+
+  expect_false(is_polars_dtype(pl$Unknown))
+  expect_true(is_polars_dtype(pl$Unknown, include_unknown = TRUE))
+})