我试图比较两列，每列来自不同的df。我有这两个：

df1
+----+-------+-------+
|Game|rev_1_t|rev_2_t|
+----+-------+-------+
|  CA|    AA |    AA |
|  FT|    B  |    C  |
+----+-------+-------+

df_prev
+----+-------+-------+
|Game|rev_1_t|rev_2_t|
+----+-------+-------+
|  CA|    C  |   AA  |  
|  FT|    B  |   C   |
+----+-------+-------+

我想比较df1中的rev_1_t和df_prev中的rev_1_t，如果有更改，则放入一个名为change的新列，如果没有更改，则使用“y”和“n”。同时，我想添加一个名为prev\u value的新列，在该列中存储df\u prev中rev\u 1\u t的先前值。版本2相同。输出为：

Output:
+----+-------+--------+------------+---------+----------+--------------+
|Game|rev_1_t| change | prev_value | rev_2_t | change_2 | prev_value_2 | 
+----+-------+--------+------------+---------+----------+--------------+
|  CA|    C  |   Y    |      C     |     AA  |   Y      |      C       |
|  FT|    B  |   Y    |      B     |     C   |   Y      |      B       |
+----+-------+--------+------------+---------+----------+--------------+

我试着做你在这里看到的，但我有不同的错误：

val change = df1.withColumn(
   "change", when (df1("rev_1_t") === df_prev("rev_1_t"), df1("rev_1_t")).otherwise(df_prev("rev_1_t"))
  .withColumn(
   "prev_value", when(df1("rev_1_t") === df_prev("rev_1_t"), "N").otherwise("Y"))