问题
I have to modify a Dataset<Row> according to some rules that are in a List<Row>.
I want to iterate over the Datset<Row> columns using Dataset.withColumn(...) as seen in the next example:
(import necesary libraries...)
SparkSession spark = SparkSession
.builder()
.appName("appname")
.config("spark.some.config.option", "some-value")
.getOrCreate();
Dataset<Row> dfToModify = spark.read().table("TableToModify");
List<Row> ListListWithInfo = new ArrayList<>(Arrays.asList());
ListWithInfo.add(0,RowFactory.create("field1", "input1", "output1", "conditionAux1"));
ListWithInfo.add(1,RowFactory.create("field1", "input1", "output1", "conditionAux2"));
ListWithInfo.add(2,RowFactory.create("field1", "input2", "output3", "conditionAux3"));
ListWithInfo.add(3,RowFactory.create("field2", "input3", "output4", "conditionAux4"));
.
.
.
for (Row row : ListWithInfo) {
String field = row.getString(0);
String input = row.getString(1);
String output = row.getString(2);
String conditionAux = row.getString(3);
dfToModify = dfToModify.withColumn(field,
when(dfToModify.col(field).equalTo(input)
.and(dfToModify.col("conditionAuxField").equalTo(conditionAux))
,output)
.otherwise(dfToModify.col(field)));
}
The code does works as it should, but when there are more than 50 "rules" in the List, the program doesn't finish and this output is shown in the screen:
0/01/27 17:48:18 INFO spark.ContextCleaner: Cleaned accumulator 1653
20/01/27 17:48:18 INFO spark.ContextCleaner: Cleaned accumulator 1650
20/01/27 17:48:18 INFO spark.ContextCleaner: Cleaned accumulator 1635
20/01/27 17:48:18 INFO spark.ContextCleaner: Cleaned accumulator 1641
20/01/27 17:48:18 INFO spark.ContextCleaner: Cleaned accumulator 1645
20/01/27 17:48:18 INFO spark.ContextCleaner: Cleaned accumulator 1646
20/01/27 17:48:18 INFO storage.BlockManagerInfo: Removed broadcast_113_piece0 on **************** in memory (size: 14.5 KB, free: 3.0 GB)
20/01/27 17:48:18 INFO storage.BlockManagerInfo: Removed broadcast_113_piece0 on ***************** in memory (size: 14.5 KB, free: 3.0 GB)
20/01/27 17:48:18 INFO spark.ContextCleaner: Cleaned accumulator 1639
20/01/27 17:48:18 INFO spark.ContextCleaner: Cleaned accumulator 1649
20/01/27 17:48:18 INFO spark.ContextCleaner: Cleaned accumulator 1651
20/01/27 17:49:18 INFO spark.ExecutorAllocationManager: Request to remove executorIds: 6
20/01/27 17:49:18 INFO cluster.YarnClientSchedulerBackend: Requesting to kill executor(s) 6
20/01/27 17:49:18 INFO cluster.YarnClientSchedulerBackend: Actual list of executor(s) to be killed is 6
20/01/27 17:49:18 INFO spark.ExecutorAllocationManager: Removing executor 6 because it has been idle for 60 seconds (new desired total will be 0)
20/01/27 17:49:19 INFO yarn.SparkRackResolver: Got an error when resolving hostNames. Falling back to /default-rack for all
20/01/27 17:49:19 INFO cluster.YarnSchedulerBackend$YarnDriverEndpoint: Disabling executor 6.
20/01/27 17:49:19 INFO scheduler.DAGScheduler: Executor lost: 6 (epoch 0)
20/01/27 17:49:19 INFO yarn.SparkRackResolver: Got an error when resolving hostNames. Falling back to /default-rack for all
20/01/27 17:49:19 INFO storage.BlockManagerMasterEndpoint: Trying to remove executor 6 from BlockManagerMaster.
20/01/27 17:49:19 INFO storage.BlockManagerMasterEndpoint: Removing block manager BlockManagerId(6, *********************, 43387, None)
20/01/27 17:49:19 INFO storage.BlockManagerMaster: Removed 6 successfully in removeExecutor
20/01/27 17:49:19 INFO cluster.YarnScheduler: Executor 6 on **************** killed by driver.
20/01/27 17:49:19 INFO spark.ExecutorAllocationManager: Existing executor 6 has been removed (new total is 0)
20/01/27 17:49:20 INFO yarn.SparkRackResolver: Got an error when resolving hostNames. Falling back to /default-rack for all
20/01/27 17:49:21 INFO yarn.SparkRackResolver: Got an error when resolving hostNames. Falling back to /default-rack for all
20/01/27 17:49:22 INFO yarn.SparkRackResolver: Got an error when resolving hostNames. Falling back to /default-rack for all
.
.
.
.
Is there any way to make it more efficient using Java Spark? (without using for loop or something similar)
回答1:
Finally I used withColumns method of Dataset<Row> objet. This method need two arguments:
.withColumns(Seq<String> ColumnsNames, Seq<Column> ColumnsValues);
And in the Seq<String> can not be duplicated.
The code is as follow:
SparkSession spark = SparkSession
.builder()
.appName("appname")
.config("spark.some.config.option", "some-value")
.getOrCreate();
Dataset<Row> dfToModify = spark.read().table("TableToModify");
List<Row> ListListWithInfo = new ArrayList<>(Arrays.asList());
ListWithInfo.add(0,RowFactory.create("field1", "input1", "output1", "conditionAux1"));
ListWithInfo.add(1,RowFactory.create("field1", "input1", "output1", "conditionAux2"));
ListWithInfo.add(2,RowFactory.create("field1", "input2", "output3", "conditionAux3"));
ListWithInfo.add(3,RowFactory.create("field2", "input3", "output4", "conditionAux4"));
.
.
.
// initialize values for fields and conditions
String field_ant = ListWithInfo.get(0).getString(0).toLowerCase();
String first_input = ListWithInfo.get(0).getString(1);
String first_output = ListWithInfo.get(0).getString(2);
String first_conditionAux = ListWithInfo.get(0).getString(3);
Column whenColumn = when(dfToModify.col(field_ant).equalTo(first_input)
.and(dfToModify.col("conditionAuxField").equalTo(lit(first_conditionAux)))
,first_output);
// lists with the names of the fields and the conditions
List<Column> whenColumnList = new ArrayList(Arrays.asList());
List<String> fieldsNameList = new ArrayList(Arrays.asList());
for (Row row : ListWithInfo.subList(1,ListWithInfo.size())) {
String field = row.getString(0);
String input = row.getString(1);
String output = row.getString(2);
String conditionAux = row.getString(3);
if (field.equals(field_ant)) {
// if field is equals to fiel_ant the new condition is added to the previous one
whenColumn = whenColumn.when(dfToModify.col(field).equalTo(input)
.and(dfToModify.col("conditionAuxField").equalTo(lit(conditionAux)))
,output);
} else {
// if field is diferent to the previous:
// close the conditions for this field
whenColumn = whenColumn.otherwise(dfToModify.col(field_ant));
// add to the lists the field(String) and the conditions (columns)
whenColumnList.add(whenColumn);
fieldsNameList.add(field_ant);
// and initialize the conditions for the new field
whenColumn = when(dfToModify.col(field).equalTo(input)
.and(dfToModify.col("branchField").equalTo(lit(branch)))
,output);
}
field_ant = field;
}
// add last values
whenColumnList.add(whenColumn);
fieldsNameList.add(field_ant);
// transform list to Seq
Seq<Column> whenColumnSeq = JavaConversions.asScalaBuffer(whenColumnList).seq();
Seq<String> fieldsNameSeq = JavaConversions.asScalaBuffer(fieldsNameList).seq();
Dataset<Row> dfModified = dfToModify.withColumns(fieldsNameSeq, whenColumnSeq);
来源：https://stackoverflow.com/questions/59953752/iterate-over-different-columns-using-withcolumn-in-java-spark