Spark DataFrame的用法.java中的flatMap

Question

我曾使用过RDD。java中的flatMap函数。现在我尝试一下DataFrames。

他们说:

public <R> RDD<R> flatMap(scala.Function1<org.apache.spark.sql.Row,
    scala.collection.TraversableOnce<R>> f, scala.reflect.ClassTag<R> evidence$4)

通过首先对其中的所有行应用函数来返回一个新的RDD

规定:在接口RDDApi中的flatMap

但是当我尝试这个，Function1，强迫我重写很多很多未实现的方法。这是我得到的:

    RDD<Row> res = df.flatMap(new Function1<Row, TraversableOnce<Row>>() {
        @Override
        public <A> Function1<Row, A> andThen(
                Function1<TraversableOnce<Row>, A> arg0) {
            // TODO Auto-generated method stub
            return null;
        }
        @Override
        public <A> Function1<Object, A> andThen$mcDD$sp(
                Function1<Object, A> arg0) {
            // TODO Auto-generated method stub
            return null;
        }
        @Override
        public <A> Function1<Object, A> andThen$mcDF$sp(
                Function1<Object, A> arg0) {
            // TODO Auto-generated method stub
            return null;
        }
        @Override
        public <A> Function1<Object, A> andThen$mcDI$sp(
                Function1<Object, A> arg0) {
            // TODO Auto-generated method stub
            return null;
        }
        @Override
        public <A> Function1<Object, A> andThen$mcDJ$sp(
                Function1<Object, A> arg0) {
            // TODO Auto-generated method stub
            return null;
        }
        @Override
        public <A> Function1<Object, A> andThen$mcFD$sp(
                Function1<Object, A> arg0) {
            // TODO Auto-generated method stub
            return null;
        }
        @Override
        public <A> Function1<Object, A> andThen$mcFF$sp(
                Function1<Object, A> arg0) {
            // TODO Auto-generated method stub
            return null;
        }
        @Override
        public <A> Function1<Object, A> andThen$mcFI$sp(
                Function1<Object, A> arg0) {
            // TODO Auto-generated method stub
            return null;
        }
        @Override
        public <A> Function1<Object, A> andThen$mcFJ$sp(
                Function1<Object, A> arg0) {
            // TODO Auto-generated method stub
            return null;
        }
        @Override
        public <A> Function1<Object, A> andThen$mcID$sp(
                Function1<Object, A> arg0) {
            // TODO Auto-generated method stub
            return null;
        }
        @Override
        public <A> Function1<Object, A> andThen$mcIF$sp(
                Function1<Object, A> arg0) {
            // TODO Auto-generated method stub
            return null;
        }
        @Override
        public <A> Function1<Object, A> andThen$mcII$sp(
                Function1<Object, A> arg0) {
            // TODO Auto-generated method stub
            return null;
        }
        @Override
        public <A> Function1<Object, A> andThen$mcIJ$sp(
                Function1<Object, A> arg0) {
            // TODO Auto-generated method stub
            return null;
        }
        @Override
        public <A> Function1<Object, A> andThen$mcJD$sp(
                Function1<Object, A> arg0) {
            // TODO Auto-generated method stub
            return null;
        }
        @Override
        public <A> Function1<Object, A> andThen$mcJF$sp(
                Function1<Object, A> arg0) {
            // TODO Auto-generated method stub
            return null;
        }
        @Override
        public <A> Function1<Object, A> andThen$mcJI$sp(
                Function1<Object, A> arg0) {
            // TODO Auto-generated method stub
            return null;
        }
        @Override
        public <A> Function1<Object, A> andThen$mcJJ$sp(
                Function1<Object, A> arg0) {
            // TODO Auto-generated method stub
            return null;
        }
        @Override
        public <A> Function1<Object, A> andThen$mcVD$sp(
                Function1<BoxedUnit, A> arg0) {
            // TODO Auto-generated method stub
            return null;
        }
        @Override
        public <A> Function1<Object, A> andThen$mcVF$sp(
                Function1<BoxedUnit, A> arg0) {
            // TODO Auto-generated method stub
            return null;
        }
        @Override
        public <A> Function1<Object, A> andThen$mcVI$sp(
                Function1<BoxedUnit, A> arg0) {
            // TODO Auto-generated method stub
            return null;
        }
        @Override
        public <A> Function1<Object, A> andThen$mcVJ$sp(
                Function1<BoxedUnit, A> arg0) {
            // TODO Auto-generated method stub
            return null;
        }
        @Override
        public <A> Function1<Object, A> andThen$mcZD$sp(
                Function1<Object, A> arg0) {
            // TODO Auto-generated method stub
            return null;
        }
        @Override
        public <A> Function1<Object, A> andThen$mcZF$sp(
                Function1<Object, A> arg0) {
            // TODO Auto-generated method stub
            return null;
        }
        @Override
        public <A> Function1<Object, A> andThen$mcZI$sp(
                Function1<Object, A> arg0) {
            // TODO Auto-generated method stub
            return null;
        }
        @Override
        public <A> Function1<Object, A> andThen$mcZJ$sp(
                Function1<Object, A> arg0) {
            // TODO Auto-generated method stub
            return null;
        }
        @Override
        public TraversableOnce<Row> apply(Row arg0) {
            // TODO Auto-generated method stub
            return null;
        }
        @Override
        public double apply$mcDD$sp(double arg0) {
            // TODO Auto-generated method stub
            return 0;
        }
        @Override
        public double apply$mcDF$sp(float arg0) {
            // TODO Auto-generated method stub
            return 0;
        }
        @Override
        public double apply$mcDI$sp(int arg0) {
            // TODO Auto-generated method stub
            return 0;
        }
        @Override
        public double apply$mcDJ$sp(long arg0) {
            // TODO Auto-generated method stub
            return 0;
        }
        @Override
        public float apply$mcFD$sp(double arg0) {
            // TODO Auto-generated method stub
            return 0;
        }
        @Override
        public float apply$mcFF$sp(float arg0) {
            // TODO Auto-generated method stub
            return 0;
        }
        @Override
        public float apply$mcFI$sp(int arg0) {
            // TODO Auto-generated method stub
            return 0;
        }
        @Override
        public float apply$mcFJ$sp(long arg0) {
            // TODO Auto-generated method stub
            return 0;
        }
        @Override
        public int apply$mcID$sp(double arg0) {
            // TODO Auto-generated method stub
            return 0;
        }
        @Override
        public int apply$mcIF$sp(float arg0) {
            // TODO Auto-generated method stub
            return 0;
        }
        @Override
        public int apply$mcII$sp(int arg0) {
            // TODO Auto-generated method stub
            return 0;
        }
        @Override
        public int apply$mcIJ$sp(long arg0) {
            // TODO Auto-generated method stub
            return 0;
        }
        @Override
        public long apply$mcJD$sp(double arg0) {
            // TODO Auto-generated method stub
            return 0;
        }
        @Override
        public long apply$mcJF$sp(float arg0) {
            // TODO Auto-generated method stub
            return 0;
        }
        @Override
        public long apply$mcJI$sp(int arg0) {
            // TODO Auto-generated method stub
            return 0;
        }
        @Override
        public long apply$mcJJ$sp(long arg0) {
            // TODO Auto-generated method stub
            return 0;
        }
        @Override
        public void apply$mcVD$sp(double arg0) {
            // TODO Auto-generated method stub
        }
        @Override
        public void apply$mcVF$sp(float arg0) {
            // TODO Auto-generated method stub
        }
        @Override
        public void apply$mcVI$sp(int arg0) {
            // TODO Auto-generated method stub
        }
        @Override
        public void apply$mcVJ$sp(long arg0) {
            // TODO Auto-generated method stub
        }
        @Override
        public boolean apply$mcZD$sp(double arg0) {
            // TODO Auto-generated method stub
            return false;
        }
        @Override
        public boolean apply$mcZF$sp(float arg0) {
            // TODO Auto-generated method stub
            return false;
        }
        @Override
        public boolean apply$mcZI$sp(int arg0) {
            // TODO Auto-generated method stub
            return false;
        }
        @Override
        public boolean apply$mcZJ$sp(long arg0) {
            // TODO Auto-generated method stub
            return false;
        }
        @Override
        public <A> Function1<A, TraversableOnce<Row>> compose(
                Function1<A, Row> arg0) {
            // TODO Auto-generated method stub
            return null;
        }
        @Override
        public <A> Function1<A, Object> compose$mcDD$sp(
                Function1<A, Object> arg0) {
            // TODO Auto-generated method stub
            return null;
        }
        @Override
        public <A> Function1<A, Object> compose$mcDF$sp(
                Function1<A, Object> arg0) {
            // TODO Auto-generated method stub
            return null;
        }
        @Override
        public <A> Function1<A, Object> compose$mcDI$sp(
                Function1<A, Object> arg0) {
            // TODO Auto-generated method stub
            return null;
        }
        @Override
        public <A> Function1<A, Object> compose$mcDJ$sp(
                Function1<A, Object> arg0) {
            // TODO Auto-generated method stub
            return null;
        }
        @Override
        public <A> Function1<A, Object> compose$mcFD$sp(
                Function1<A, Object> arg0) {
            // TODO Auto-generated method stub
            return null;
        }
        @Override
        public <A> Function1<A, Object> compose$mcFF$sp(
                Function1<A, Object> arg0) {
            // TODO Auto-generated method stub
            return null;
        }
        @Override
        public <A> Function1<A, Object> compose$mcFI$sp(
                Function1<A, Object> arg0) {
            // TODO Auto-generated method stub
            return null;
        }
        @Override
        public <A> Function1<A, Object> compose$mcFJ$sp(
                Function1<A, Object> arg0) {
            // TODO Auto-generated method stub
            return null;
        }
        @Override
        public <A> Function1<A, Object> compose$mcID$sp(
                Function1<A, Object> arg0) {
            // TODO Auto-generated method stub
            return null;
        }
        @Override
        public <A> Function1<A, Object> compose$mcIF$sp(
                Function1<A, Object> arg0) {
            // TODO Auto-generated method stub
            return null;
        }
        @Override
        public <A> Function1<A, Object> compose$mcII$sp(
                Function1<A, Object> arg0) {
            // TODO Auto-generated method stub
            return null;
        }
        @Override
        public <A> Function1<A, Object> compose$mcIJ$sp(
                Function1<A, Object> arg0) {
            // TODO Auto-generated method stub
            return null;
        }
        @Override
        public <A> Function1<A, Object> compose$mcJD$sp(
                Function1<A, Object> arg0) {
            // TODO Auto-generated method stub
            return null;
        }
        @Override
        public <A> Function1<A, Object> compose$mcJF$sp(
                Function1<A, Object> arg0) {
            // TODO Auto-generated method stub
            return null;
        }
        @Override
        public <A> Function1<A, Object> compose$mcJI$sp(
                Function1<A, Object> arg0) {
            // TODO Auto-generated method stub
            return null;
        }
        @Override
        public <A> Function1<A, Object> compose$mcJJ$sp(
                Function1<A, Object> arg0) {
            // TODO Auto-generated method stub
            return null;
        }
        @Override
        public <A> Function1<A, BoxedUnit> compose$mcVD$sp(
                Function1<A, Object> arg0) {
            // TODO Auto-generated method stub
            return null;
        }
        @Override
        public <A> Function1<A, BoxedUnit> compose$mcVF$sp(
                Function1<A, Object> arg0) {
            // TODO Auto-generated method stub
            return null;
        }
        @Override
        public <A> Function1<A, BoxedUnit> compose$mcVI$sp(
                Function1<A, Object> arg0) {
            // TODO Auto-generated method stub
            return null;
        }
        @Override
        public <A> Function1<A, BoxedUnit> compose$mcVJ$sp(
                Function1<A, Object> arg0) {
            // TODO Auto-generated method stub
            return null;
        }
        @Override
        public <A> Function1<A, Object> compose$mcZD$sp(
                Function1<A, Object> arg0) {
            // TODO Auto-generated method stub
            return null;
        }
        @Override
        public <A> Function1<A, Object> compose$mcZF$sp(
                Function1<A, Object> arg0) {
            // TODO Auto-generated method stub
            return null;
        }
        @Override
        public <A> Function1<A, Object> compose$mcZI$sp(
                Function1<A, Object> arg0) {
            // TODO Auto-generated method stub
            return null;
        }
        @Override
        public <A> Function1<A, Object> compose$mcZJ$sp(
                Function1<A, Object> arg0) {
            // TODO Auto-generated method stub
            return null;
        }
    }, evidence$4);

这看起来很奇怪，但我继续使evidence$4为:

ClassTag<Row> evidence$4 = scala.reflect.ClassTag$.MODULE$.apply(Row.class);

我的意图是只是玩弄flatMap(当然是在DataFrames上，而不是在RDD上)。所以我不需要对Row做任何改变。

所以我想我只需要在apply方法中进行更改。

    @Override
    public TraversableOnce<Row> apply(Row arg0) {
        // TODO Auto-generated method stub
        return null;
    }

但是，我该如何从Row中得到TraversableOnce<Row>呢?

另外，我正在尝试的方法是正确的吗?还是我错过了什么?

我使用Apache Spark 1.3.1

Answer 1

您应该做如下操作:

RDD<Row> res = df.flatMap(new AbstractFunction1<Row, TraversableOnce<Row>>() {
  public TraversableOnce<Row> apply(Row row) {
    return new ListSet<Row>().$plus(row); //Note the updated list is returned from $plus()
  }
}, evidence$4);

这将类似于map，只是有更多的自由来改变。例如，要过滤掉东西，您可以在想要返回时返回空的new ListSet<Row>()，或者保持当前的行为。flatMap非常灵活。

(从Java集合到Scala集合的转换似乎并不简单)