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From HyukjinKwon <...@git.apache.org>
Subject [GitHub] spark pull request #15513: [SPARK-17963][SQL][Documentation] Add examples (e...
Date Sat, 29 Oct 2016 00:30:30 GMT
Github user HyukjinKwon commented on a diff in the pull request:

    https://github.com/apache/spark/pull/15513#discussion_r85628075
  
    --- Diff: sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/windowExpressions.scala
---
    @@ -401,22 +408,29 @@ case class Lead(input: Expression, offset: Expression, default:
Expression)
     }
     
     /**
    - * The Lag function returns the value of 'x' at the 'offset'th row before the current
row in
    + * The Lag function returns the value of `input` at the `offset`th row before the current
row in
      * the window. Offsets start at 0, which is the current row. The offset must be constant
    - * integer value. The default offset is 1. When the value of 'x' is null at the 'offset'th
row,
    - * null is returned. If there is no such offset row, the default expression is evaluated.
    + * integer value. The default offset is 1. When the value of `input` is null at the `offset`th
row,
    + * null is returned. If there is no such offset row, the `default` expression is evaluated.
      *
    - * @param input expression to evaluate 'offset' rows before the current row.
    + * @param input expression to evaluate `offset` rows before the current row.
      * @param offset rows to jump back in the partition.
      * @param default to use when the offset row does not exist.
      */
    -@ExpressionDescription(usage =
    -  """_FUNC_(input, offset, default) - LAG returns the value of 'x' at the 'offset'th
row
    -     before the current row in the window.
    -     The default value of 'offset' is 1 and the default value of 'default' is null.
    -     If the value of 'x' at the 'offset'th row is null, null is returned.
    -     If there is no such offset row (e.g. when the offset is 1, the first row of the
window
    -     does not have any previous row), 'default' is returned.""")
    +@ExpressionDescription(
    +  usage = """
    +    _FUNC_(input[, offset[, default]]) - Returns the value of `input` at the `offset`th
row
    +      before the current row in the window. The default value of `offset` is 1 and the
default
    +      value of `default` is null. If the value of `input` at the `offset`th row is null,
    +      null is returned. If there is no such offset row (e.g., when the offset is 1, the
first
    +      row of the window does not have any previous row), `default` is returned.
    +  """,
    +  extended = """
    +    Arguments:
    +      input - an expression of any type.
    +      offset - a numeric expression. Default is 1.
    +      default - an expression of any type. Default is null.
    --- End diff --
    
    ```scala
           {
          val df = Seq((1, "1"), (2, "2"), (1, "1"), (2, "2")).toDF("key", "value")
            .selectExpr("array(value) as value", "key")
          df.select(
            lag("value", 1).over(Window.partitionBy($"key").orderBy($"value"))).show()
        }
        {
          val df = Seq((1, "1"), (2, "2"), (1, "1"), (2, "2")).toDF("key", "value")
            .selectExpr("struct(value) as value", "key")
          df.select(
            lag("value", 1).over(Window.partitionBy($"key").orderBy($"value"))).show()
        }
    ```


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