Github user sun-rui commented on a diff in the pull request: https://github.com/apache/spark/pull/8920#discussion_r40645685 --- 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)) + jcols <- lapply(resCols, function(c) { --- End diff -- can call arrange() or orderBy() here.
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