HyukjinKwon commented on a change in pull request #27433:
[SPARK-30682][SPARKR][SQL] Add SparkR interface for higher order functions
URL: https://github.com/apache/spark/pull/27433#discussion_r373898606
##########
File path: R/pkg/R/functions.R
##########
@@ -3281,6 +3322,126 @@ setMethod("row_number",
###################### Collection functions######################
+#' Create o.a.s.sql.expressions.UnresolvedNamedLambdaVariable,
+#' convert it to o.s.sql.Column and wrap with R Column.
+#' Used by higher order functions.
+#'
+#' @param ... character of length = 1
+#' if length(...) > 1 then argument is interpreted as a nested
+#' Column, for example \code{unresolved_named_lambda_var("a", "b", "c")}
+#' yields unresolved \code{a.b.c}
+#' @return Column object wrapping JVM UnresolvedNamedLambdaVariable
+unresolved_named_lambda_var <- function(...) {
+ jc <- sparkR.newJObject(
+ "org.apache.spark.sql.Column",
+ sparkR.newJObject(
+
"org.apache.spark.sql.catalyst.expressions.UnresolvedNamedLambdaVariable",
+ list(...)
+ )
+ )
+ column(jc)
+}
+
+#' Create o.a.s.sql.expressions.LambdaFunction corresponding
+#' to transformation described by func.
+#' Used by higher order functions.
+#'
+#' @param fun R \code{function} (unary, binary or ternary)
+#' that transforms \code{Columns} into a \code{Column}
+#' @param expected_nargs numeric a vector of the expected
+#' number of arguments. Used for validation
+#' @return JVM \code{LambdaFunction} object
+create_lambda <- function(fun, expected_nargs) {
+ as_jexpr <- function(x) callJMethod(x@jc, "expr")
+
+ # Process function arguments
+ parameters <- formals(fun)
+ nparameters <- length(parameters)
+
+ stopifnot(nparameters %in% expected_nargs)
Review comment:
cc @felixcheung, @falaki, @shivaram, this one, I am not sure about it yet
(see https://github.com/apache/spark/pull/27406#discussion_r373896752 for more
details).
Also, given that JVM throws an error as below:
```
: org.apache.spark.sql.AnalysisException: The number of lambda function
arguments '2' does not match the number of arguments expected by the higher
order function '1'.;
```
if we use `captureJVMException` (see
https://github.com/apache/spark/pull/27433/files#r373898428), I assume it will
show R-friendly error messages.
For a simple checking in R side, I am supportive but I am less sure for such
complex checking. I tend to think it's better to have less codes if the error
message is already readable at the current moment.
We should find a better way to handle the error messages in general (e.g.,
at
[utils.R#L820-L872](https://github.com/apache/spark/blob/master/R/pkg/R/utils.R#L820-L872)).
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