Merge pull request apache#198 from cafreeman/sparkr-sql

`selectExpr`

pkg/NAMESPACE

@@ -100,6 +100,7 @@ exportMethods("columns",
               "schema",
               "sortDF",
               "select",
+              "selectExpr",
               "toRDD",
               "where")
 

pkg/R/DataFrame.R

@@ -607,6 +607,36 @@ setMethod("select", signature(x = "DataFrame", col = "Column"),
             dataFrame(sdf)
           })
 
+#' SelectExpr
+#'
+#' Select from a DataFrame using a set of SQL expressions.
+#'
+#' @param x A DataFrame to be selected from.
+#' @param expr A string containing a SQL expression
+#' @param ... Additional expressions
+#' @return A DataFrame
+#' @rdname selectExpr
+#' @export
+#' @examples
+#'\dontrun{
+#' sc <- sparkR.init()
+#' sqlCtx <- sparkRSQL.init(sc)
+#' path <- "path/to/file.json"
+#' df <- jsonFile(sqlCtx, path)
+#' selectExpr(df, "col1", "(col2 * 5) as newCol")
+#' }
+setGeneric("selectExpr", function(x, expr, ...) { standardGeneric("selectExpr") })
+
+#' @rdname selectExpr
+#' @export
+setMethod("selectExpr",
+          signature(x = "DataFrame", expr = "character"),
+          function(x, expr, ...) {
+            exprList <- list(expr, ...)
+            sdf <- callJMethod(x@sdf, "selectExpr", listToSeq(exprList))
+            dataFrame(sdf)
+          })
+
 #' SortDF 
 #'
 #' Sort a DataFrame by the specified column(s).

pkg/inst/tests/test_sparkSQL.R

@@ -260,6 +260,17 @@ test_that("select with column", {
   expect_true(count(df2) == 3)
 })
 
+test_that("selectExpr() on a DataFrame", {
+  df <- jsonFile(sqlCtx, jsonPath)
+  selected <- selectExpr(df, "age * 2")
+  expect_true(names(selected) == "(age * 2)")
+  expect_equal(collect(selected), collect(select(df, df$age * 2L)))
+
+  selected2 <- selectExpr(df, "name as newName", "abs(age) as age")
+  expect_equal(names(selected2), c("newName", "age"))
+  expect_true(count(selected2) == 3)
+})
+
 test_that("column calculation", {
   df <- jsonFile(sqlCtx, jsonPath)
   d <- collect(select(df, alias(df$age + 1, "age2")))