Cascading - regex parser - wrong number of fields

Question

Starting to play with Cascading on Amazon EMR, have managed to get it running BUT falling at a fairly simple hurdle and I was hoping someone could shed some light on it.

My code:

import java.util.Properties;

import cascading.flow.Flow;
import cascading.flow.FlowDef;
import cascading.flow.hadoop.HadoopFlowConnector;
import cascading.pipe.Pipe;
import cascading.property.AppProps;
import cascading.scheme.hadoop.TextLine;
import cascading.tap.Tap;
import cascading.tap.hadoop.Hfs;
import cascading.tuple.Fields;
import cascading.operation.regex.RegexParser;
import cascading.pipe.Each;
import cascading.tap.SinkMode;

public class Main
  {
  public static void
  main( String[] args )
    {
    String inPath = args[ 0 ];
    String outPath = args[ 1 ];

    Properties properties = new Properties();
    AppProps.setApplicationJarClass( properties, Main.class );
    HadoopFlowConnector flowConnector = new HadoopFlowConnector( properties );

    // create the source tap
    TextLine sourceScheme = new TextLine(new Fields("line"));
    Tap inTap = new Hfs( sourceScheme, inPath );

    // create the sink tap
    TextLine sinkScheme = new TextLine( new Fields("custid", "movieids"));
    Tap outTap = new Hfs( sinkScheme, outPath, SinkMode.REPLACE );

    Fields filmFields = new Fields("custid", "movieids");

    String filmRegex = "([0-9]:*[,.]*)";

    RegexParser parser = new RegexParser(filmFields, filmRegex);

    Pipe importPipe = new Each("import", new Fields("line"), parser, Fields.RESULTS );

    // connect the taps, pipes, etc., into a flow
    Flow parsedFlow = new HadoopFlowConnector(properties).connect(inTap, outTap, importPipe);

    // run the flow
    parsedFlow.start();
    parsedFlow.complete();
    }
  }

My input (no empty lines):

1:2

2:4

5:1

3:9

My output:

Task TASKID="task_201305241444_0003_m_000000" TASK_TYPE="MAP" TASK_STATUS="FAILED" FINISH_TIME="1369408133954" ERROR="cascading\.tuple\.TupleException: operation added the wrong number of fields, expected: ['custid', 'movieids'], got result size: 1
    at cascading\.tuple\.TupleEntryCollector\.add(TupleEntryCollector\.java:82)
    at cascading\.operation\.regex\.RegexParser\.onFoundGroups(RegexParser\.java:168)
    at cascading\.operation\.regex\.RegexParser\.operate(RegexParser\.java:151)
    at cascading\.flow\.stream\.FunctionEachStage\.receive(FunctionEachStage\.java:99)
    at cascading\.flow\.stream\.FunctionEachStage\.receive(FunctionEachStage\.java:39)
    at cascading\.flow\.stream\.SourceStage\.map(SourceStage\.java:102)
    at cascading\.flow\.stream\.SourceStage\.run(SourceStage\.java:58)
    at cascading\.flow\.hadoop\.FlowMapper\.run(FlowMapper\.java:127)
    at org\.apache\.hadoop\.mapred\.MapTask\.runOldMapper(MapTask\.java:441)
    at org\.apache\.hadoop\.mapred\.MapTask\.run(MapTask\.java:377)
    at org\.apache\.hadoop\.mapred\.Child$4\.run(Child\.java:255)
    at java\.security\.AccessController\.doPrivileged(Native Method)
    at javax\.security\.auth\.Subject\.doAs(Subject\.java:396)
    at org\.apache\.hadoop\.security\.UserGroupInformation\.doAs(UserGroupInformation\.java:1132)
    at org\.apache\.hadoop\.mapred\.Child\.main(Child\.java:249)

The reg ex checks out fine at http://regexpal.com/

Thanks a lot

Duncan

score 1 · Answer 1 · answered May 24 '13 at 19:59

You get an exception because your regular expression yields one result, where two result fields are excepted (namely "custid" and "movieids"), because the regular expression contains just a single group (...).

If you just want to split at the colon, either use an expression with 2 groups, for example:

String filmRegex = "(\\d):(\\d)";

or \d+, respectively, if your numbers can have more than one digit.

Or, more easily, just split the input data into its fields automatically when reading from the file by using a TextDelimited input scheme:

Scheme sourceScheme = new TextDelimited(new Fields("custid", "movieids"), ":");

Cascading - regex parser - wrong number of fields

1 Answers1