val rdd1 = sc.parallelize(
Seq(("one two three four five six seven"), 
("one two three four five six seven"), 
("one two three four five six seven")))

然后

rdd1.map(_.split(" ")).collect

结果
Array[Array[String]] = Array(Array(one, two, three, four, five, six, seven),
Array(one, two, three, four, five, six, seven),
Array(one, two, three, four, five, six, seven))

rdd1.flatMap(_.split(" ")).collect

结果
Array[String] = Array(one, two, three, four, five, six, seven,
one, two, three, four, five, six, seven,
one, two, three, four, five, six, seven)