How do I compare each column in a table using Data

问题:

This question already has an answer here:

• How do I compare each column in a table using DataFrame by Scala 2 answers

The question I asked before is as follows. Last question

Table 1 -- ID pairs table

Table 2 -- Attribute table

Table 3

For example, id1 and id2 have different color and size, so the id1 and id2 row(2nd row in Table 3) has "id1 id2 0 0";

id1 and id3 have same color and different size, so the id1 and id3 row(3nd row in Table 3) has "id1 id3 1 0";

Same attribute---1 Different attribute---0

But, what if I do not know how many attribute columns in Table2; how can I make it? Such as I do not know the column name color or size. Maybe there is another column called brand. Then how can I get Table3?

回答1:

The following solution should work for any unknown number of attributes in Table2. I have edited the answer from your Last Question

val t1 = List(
  ("id1","id2"),
  ("id1","id3"),
  ("id2","id3")
).toDF("id_x", "id_y")

val t2 = List(
  ("id1","blue","m","brand1"),
  ("id2","red","s","brand1"),
  ("id3","blue","s","brand2")
).toDF("id", "color", "size", "brand")

val outSchema = t2.columns.tail

var t3 = t1
  .join(t2.as("x"), $"id_x" === $"x.id", "inner")
  .join(t2.as("y"), $"id_y" === $"y.id", "inner")

  for(columnName <- outSchema){
    t3 = t3.withColumn(columnName+"s", when(col(s"x.$columnName") === col(s"y.$columnName"),1).otherwise(0))
      .drop(columnName)
      .drop("id")
      .withColumnRenamed(columnName+"s", columnName)

  }
t3.show(false)

The final output is

+----+----+-----+----+-----+
|id_x|id_y|color|size|brand|
+----+----+-----+----+-----+
|id1 |id2 |0    |0   |1    |
|id1 |id3 |1    |0   |0    |
|id2 |id3 |0    |1   |0    |
+----+----+-----+----+-----+

The solution should work for any unknown number of attributes.