[SPARK-23291][SQL][R][BRANCH-2.3] R's substr should not reduce starting position by 1 when calling Scala API

R/pkg/R/column.R

@@ -164,12 +164,18 @@ setMethod("alias",
 #' @aliases substr,Column-method
 #'
 #' @param x a Column.
-#' @param start starting position.
+#' @param start starting position. It should be 1-base.
 #' @param stop ending position.
+#' @examples
+#' \dontrun{
+#' df <- createDataFrame(list(list(a="abcdef")))
+#' collect(select(df, substr(df$a, 1, 4))) # the result is `abcd`.
+#' collect(select(df, substr(df$a, 2, 4))) # the result is `bcd`.
+#' }
 #' @note substr since 1.4.0
 setMethod("substr", signature(x = "Column"),
           function(x, start, stop) {
-            jc <- callJMethod(x@jc, "substr", as.integer(start - 1), as.integer(stop - start + 1))
+            jc <- callJMethod(x@jc, "substr", as.integer(start), as.integer(stop - start + 1))
             column(jc)
           })
 

R/pkg/tests/fulltests/test_sparkSQL.R

@@ -1649,6 +1649,7 @@ test_that("string operators", {
   expect_false(first(select(df, startsWith(df$name, "m")))[[1]])
   expect_true(first(select(df, endsWith(df$name, "el")))[[1]])
   expect_equal(first(select(df, substr(df$name, 1, 2)))[[1]], "Mi")
+  expect_equal(first(select(df, substr(df$name, 4, 6)))[[1]], "hae")
   if (as.numeric(R.version$major) >= 3 && as.numeric(R.version$minor) >= 3) {
     expect_true(startsWith("Hello World", "Hello"))
     expect_false(endsWith("Hello World", "a"))

docs/sparkr.md

@@ -663,3 +663,7 @@ You can inspect the search path in R with [`search()`](https://stat.ethz.ch/R-ma
  - The `stringsAsFactors` parameter was previously ignored with `collect`, for example, in `collect(createDataFrame(iris), stringsAsFactors = TRUE))`. It has been corrected.
  - For `summary`, option for statistics to compute has been added. Its output is changed from that from `describe`.
  - A warning can be raised if versions of SparkR package and the Spark JVM do not match.
+
+## Upgrading to SparkR 2.3.1 and above
+
+ - In SparkR 2.3.0 and earlier, the `start` parameter of `substr` method was wrongly subtracted by one and considered as 0-based. This can lead to inconsistent substring results and also does not match with the behaviour with `substr` in R. In version 2.3.1 and later, it has been fixed so the `start` parameter of `substr` method is now 1-base. As an example, `substr(lit('abcdef'), 2, 4))` would result to `abc` in SparkR 2.3.0, and the result would be `bcd` in SparkR 2.3.1.