Github user sun-rui commented on a diff in the pull request:
https://github.com/apache/spark/pull/8920#discussion_r40646379
--- Diff: R/pkg/R/DataFrame.R ---
@@ -1848,3 +1848,78 @@ setMethod("crosstab",
sct <- callJMethod(statFunctions, "crosstab", col1, col2)
collect(dataFrame(sct))
})
+
+#' Sort
+#'
+#' Sort a DataFrame by the specified column(s).
+#'
+#' @param x A DataFrame to be sorted.
+#' @param by A character column or Column Object indicating the field to
sort on.
+#' If sorting column is a Column object, we need to embrace the
column with asc or desc
+#' keyword. The 'decreasing' argument does not apply to Column
Object. It only applies to
+#' character column names
+#' @param decreasing Orderings for each sorting column
+#' @param ... Additional sorting fields
+#' @return A DataFrame where elements are sorted by input sorting columns.
+#' @rdname sort
+#' @name sort
+#' @aliases orderby
+#' @export
+#' @examples
+#'\dontrun{
+#' sc <- sparkR.init()
+#' sqlContext <- sparkRSQL.init(sc)
+#' path <- "path/to/file.json"
+#' df <- jsonFile(sqlContext, path)
+#' sort(df, col="col1")
+#' sort(df, decreasing=FALSE, "col2")
+#' sort(df, decreasing=TRUE, "col1")
+#' sort(df, c(TRUE,FALSE), "col1","col2")
+#' sort(df, col=list(asc(df$col1), desc(df$col2)))
+#' sort(df, col=desc(df$col1))
+#' }
+setMethod("sort",
+ signature(x = "DataFrame"),
+ function(x, decreasing=FALSE, col, ...) {
+
+ # all sorting columns
+ by <- c(col, ...)
+
+ if (class(by) == "character"){
+ if (length(decreasing) == 1){
+ # in case only 1 boolean argument - decreasing value is
specified, it will be used for all columns
+ decreasing <- rep(decreasing,length(by))
+ } else if (length(decreasing) != length(by)){
+ stop("Arguments 'col' and 'decreasing' must have the same
length")
+ }
+
+ # creates a string array by replacing TRUE/FALSE
correspondingly by "desc"/"asc"
+ sortOrder <- ifelse (decreasing == FALSE, "asc", decreasing)
+ sortOrder <- ifelse (decreasing == TRUE, "desc", sortOrder)
+
+ # concatenates dataframe with the column names, example:
c("x$Species", "x$Petal_Width")
+ colDFConcat <- paste("x", by, sep = "$")
+
+ # embraces columns with order - asc/desc
+ # example: c("asc(x$Species)", "desc(x$Petal_Length)" )
+ colDFOrderConcat <- paste(sortOrder, "(", colDFConcat, ")",
collapse = ",")
+
+ # concatenates all ordered columns to a list
+ # example: "list(asc(x$Species), desc(x$Petal_Length))"
+ colDFOrderConcatList <- paste("list(", colDFOrderConcat,
")", collapse = "")
+
+ # builds columns of type Column, example: [[1]] Column
Species ASC
+ # [[2]] Column
Petal_Length DESC
+ resCols <- eval(parse(t=colDFOrderConcatList))
--- End diff --
Instead of building expressions and use eval(), I would prefer something
like:
lapply(seq_len(length(decreasing)), function(i) {
if (decreasing[[i]]) {
desc(column(x, col[[i]]))
} else {
asc(column(x, col[ii]])
}
}
---
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