我有两个数据帧，代表同一个人的两个不同时间段。我想了解，对于每一行，两个数据帧的5（固定）列是否有任何变化。
之前：
+--+------+------+------+------+------+------+
|id| sport| var1| var2| var3| var4| var5|
+--+------+------+------+------+------+------+
| 1|soccer|330234| | | | |
| 2|soccer| null| null| null| null| null|
| 3|soccer|330101| | | | |
| 4|soccer| null| null| null| null| null|
| 5|soccer| null| null| null| null| null|
| 6|soccer| null| null| null| null| null|
| 7|soccer| null| null| null| null| null|
| 8|soccer|330024|330401| | | |
| 9|soccer|330055|330106| | | |
|10|soccer| null| null| null| null| null|
|11|soccer|390027| | | | |
|12|soccer| null| null| null| null| null|
|13|soccer|330101| | | | |
|14|soccer|330059| | | | |
|15|soccer| null| null| null| null| null|
|16|soccer|140242|140281| | | |
|17|soccer|330214| | | | |
|18|soccer| | | | | |
|19|soccer|330055|330196| | | |
|20|soccer|210022| | | | |
+--+------+------+------+------+------+------+
之后：
+--+------+------+------+------+------+------+
|id| sport| var1| var2| var3| var4| var5|
+--+------+------+------+------+------+------+
| 1|soccer|330234| | | | |
| 2|soccer| null| null| null| null| null|
| 3|soccer|330101| | | | |
| 4|soccer| null| null| null| null| null|
| 5|soccer| null| null| null| null| null|
| 6|soccer| null| null| null| null| null|
| 7|soccer| null| null| null| null| null|
| 8|soccer| null| null| null| null| null|
| 9|soccer|330106| | | | |
|10|soccer| null| null| null| null| null|
|11|soccer|390027| | | | |
|12|soccer| null| null| null| null| null|
|13|soccer| null| null| null| null| null|
|14|soccer|330128|330331|330106|330059| |
|15|soccer| null| null| null| null| null|
|16|soccer|140242|140281|140010| | |
|17|soccer|330214| | | | |
|18|soccer| null| null| null| null| null|
|19|soccer|330196| | | | |
|20|soccer|210022| | | | |
+--+------+------+------+------+------+------+
我知道如何扫描属于一行的列中的差异，但我不知道如何比较两个不同数据帧的行。
理想的输出是：
+--+------+------+
|id| sport| diff|
+--+------+------+
| 1|soccer| 0|
| 2|soccer| 0|
| 3|soccer| 0|
| 4|soccer| 0|
| 5|soccer| 0|
| 6|soccer| 0|
| 7|soccer| 0|
| 8|soccer| 1|
| 9|soccer| 1|
|10|soccer| 0|
|11|soccer| 0|
|12|soccer| 0|
|13|soccer| 1|
|14|soccer| 1|
|15|soccer| 0|
|16|soccer| 1|
|17|soccer| 0|
|18|soccer| 0|
|19|soccer| 1|
|20|soccer| 0|
你的意思是这样的吗？让我们从示例数据开始：
val before = Seq(
(1, "soccer", Some(1), Some(2), Some(3), Some(4), None),
(2, "soccer", None, Some(0), None, None, Some(0)),
(3, "soccer", None, None, None, None, None)
).toDF("id", "sport", "var1", "var2", "var3", "var4", "var5")
val after = Seq(
(1, "soccer", Some(1), Some(2), Some(3), Some(4), None), // Zero diffs
(2, "soccer", Some(1), Some(0), None, None, Some(0)), // One diff
(3, "soccer", Some(1), Some(1), Some(1), Some(1), Some(1)) // Five diffs
).toDF("id", "sport", "var1", "var2", "var3", "var4", "var5")
生成一个计算差异的表达式：
// Extract var columns
val varCols = before.columns.drop(2)
// Generate a list of exprs
// CAST(NOT(before.var1 <=> after.var1) AS INT)
val equalsExprs = varCols.map(
c => not(col(s"before.$c") <=> col(s"after.$c")).cast("int").alias(s"${c}_ne"))
// SUM
val diff = equalsExprs.foldLeft(lit(0))(_ + _).alias("diff")
它将治疗：
- 两个NULL相等
- 任意值和NULL不相等
- 两个非NULL值-标准类型相等
加入并选择表达式：
val diffs = before.as("before").join(after.as("after"), Seq("id", "sport"))
.select($"id", $"sport", diff)
diffs.show
// +---+------+----+
// | id| sport|diff|
// +---+------+----+
// | 1|soccer| 0|
// | 2|soccer| 1|
// | 3|soccer| 5|
// +---+------+----+