我有一个数据帧列表：val dfs = Seq [df1，df2，df3，df4，....]
df1：
+--------+--------+
| Value1 | Amount |
+--------+--------+
| A1 | 2000 |
+--------+--------+
| B1 | 100 |
+--------+--------+
| C1 | 349 |
+--------+--------+
DF2
+--------+--------+
| value1 | Amount |
+--------+--------+
| A2 | 20 |
+--------+--------+
| B2 | 34 |
+--------+--------+
| C2 | 56 |
+--------+--------+
DF3：
+--------+--------+--------+
| value1 | value2 | amount |
+--------+--------+--------+
| A3 | CA | 234 |
+--------+--------+--------+
| B3 | AZ | 324 |
+--------+--------+--------+
| C3 | NY | 213 |
+--------+--------+--------+
DF4：
+--------+--------+--------+
| value1 | value2 | amount |
+--------+--------+--------+
| A | null | 300 |
+--------+--------+--------+
| B | null | 400 |
+--------+--------+--------+
| C | null | 200 |
+--------+--------+--------+
| A1 | null | 2000 |
+--------+--------+--------+
| B1 | null | 100 |
+--------+--------+--------+
| C1 | null | 349 |
+--------+--------+--------+
| A2 | null | 20 |
+--------+--------+--------+
| B2 | null | 34 |
+--------+--------+--------+
| C2 | null | 56 |
+--------+--------+--------+
| A3 | CA | 234 |
+--------+--------+--------+
| B3 | AZ | 324 |
+--------+--------+--------+
| C3 | NY | 213 |
+--------+--------+--------+
我希望将列表中的所有数据帧合并，但由于列数不同，无法执行此操作。 对于unionAll：当我做unionall时 dfs.reduce（ unionall ）。显示（）
而不是unionall前三个数据帧，将第四列添加为null并使用df4执行unionall。有人可以帮助我如何做，unionall以通用的方式。从列表中获取数据帧
如何在循环条件下对具有不同列的数据帧列表进行unionAll操作？
预期产出：
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