Github user felixcheung commented on a diff in the pull request:
https://github.com/apache/spark/pull/11336#discussion_r84189253
--- Diff: R/pkg/R/column.R ---
@@ -29,38 +31,66 @@ setOldClass("jobj")
#' @rdname column
#'
#' @slot jc reference to JVM SparkDataFrame column
+#' @slot df the parent SparkDataFrame of the Column object
#' @export
#' @note Column since 1.4.0
setClass("Column",
- slots = list(jc = "jobj"))
+ slots = list(jc = "jobj", df = "SparkDataFrameOrNull"))
#' A set of operations working with SparkDataFrame columns
#' @rdname columnfunctions
#' @name columnfunctions
NULL
-
-setMethod("initialize", "Column", function(.Object, jc) {
+setMethod("initialize", "Column", function(.Object, jc, df) {
.Object@jc <- jc
+
+ # Some Column objects don't have any referencing DataFrame. In such
case, df will be NULL.
+ if (missing(df)) {
+ df <- NULL
+ }
+ .Object@df <- df
.Object
})
+#' @rdname show
+setMethod("show", signature = "Column", function(object) {
+ MAX_ELEMENTS <- 20
+ head.df <- head(object, MAX_ELEMENTS)
+
+ if (length(head.df) == 0) {
+ colname <- callJMethod(object@jc, "toString")
+ cat(paste0(colname, "\n"))
+ cat(paste0("<Empty column>\n"))
+ } else {
+ show(head.df)
+ }
+ if (length(head.df) == MAX_ELEMENTS) {
+ cat(paste0("\b...\nDisplaying up to ", as.character(MAX_ELEMENTS), "
elements only."))
+ }
+})
+
+#' @rdname head
+setMethod("head",
+ signature = "Column",
--- End diff --
There are more than 1 in the file...
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