[jira] [Updated] (MAPREDUCE-6837) Add an equivalent to Crunch's Pair class

["Daniel Templeton (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/MAPREDUCE-6837?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Daniel Templeton updated MAPREDUCE-6837:
----------------------------------------
    Description: 
Crunch has this great {{Pair}} class (https://crunch.apache.org/apidocs/0.14.0/org/apache/crunch/Pair.html) that saves one from constantly implementing composite writables.  It seems silly that we still don't have an equivalent in MR.

I would like to see a new class with the following API:

{code}
package org.apache.hadoop.io;

public class CompositeWritable<P extends WritableComparable, S extends WritableComparable> implements WritableComparable<CompositeWritable> {
  public CompositeWritable(P primary, S secondary);
  public P getPrimary();
  public void setPrimary(P primary);
  public S getSecondary();
  public void setSecondary(S secondary);

  // Return true if both primaries and both secondaries are equal
  public boolean equals(CompositeWritable o);

  // Return the primary's hash code
  public long hashCode();

  // Sort first by primary and then by secondary
  public int compareTo(CompositeWritable o);

  public void readFields(DataInput in);
  public void write(DataOutput out);
}
{code}

With such a class, implementing a secondary sort would mean just implementing a custom grouping comparator.  That comparator could also be implemented as part of this JIRA:

{code}
package org.apache.hadoop.io;

public class CompositeGroupingComparator extends WritableComparator {
  ...
}
{code}

Or some such.

Crunch also provides {{Tuple3}}, {{Tuple4}}, and {{TupleN}} classes, but I don't think we need to add equivalents.  If someone really wants that capability, they can nest composite keys.

Don't forget to add unit tests!

  was:
Crunch has this great {{Pair}} class (https://crunch.apache.org/apidocs/0.14.0/org/apache/crunch/Pair.html) that save you from constantly implementing composite writables.  It seems silly that we still don't have an equivalent in MR.

I would like to see a new class with the following API:

{code}
package org.apache.hadoop.io;

public class CompositeWritable<P extends WritableComparable, S extends WritableComparable> implements WritableComparable<CompositeWritable> {
  public CompositeWritable(P primary, S secondary);
  public P getPrimary();
  public void setPrimary(P primary);
  public S getSecondary();
  public void setSecondary(S secondary);

  // Return true if both primaries and both secondaries are equal
  public boolean equals(CompositeWritable o);

  // Return the primary's hash code
  public long hashCode();

  // Sort first by primary and then by secondary
  public int compareTo(CompositeWritable o);

  public void readFields(DataInput in);
  public void write(DataOutput out);
}
{code}

With such a class, implementing a secondary sort would mean just implementing a custom grouping comparator.  That comparator could be implemented as part of this JIRA:

{code}
package org.apache.hadoop.io;

public class CompositeGroupingComparator extends WritableComparator {
  ...
}
{code}

Or some such.

Crunch also provides {{Tuple3}}, {{Tuple4}}, and {{TupleN}} classes, but I don't think we need to add equivalents.  If someone really wants that capability, they can nest composite keys.

Don't forget to add unit tests!


> Add an equivalent to Crunch's Pair class
> ----------------------------------------
>
>                 Key: MAPREDUCE-6837
>                 URL: https://issues.apache.org/jira/browse/MAPREDUCE-6837
>             Project: Hadoop Map/Reduce
>          Issue Type: Improvement
>          Components: mrv2
>            Reporter: Daniel Templeton
>              Labels: newbie++
>
> Crunch has this great {{Pair}} class (https://crunch.apache.org/apidocs/0.14.0/org/apache/crunch/Pair.html) that saves one from constantly implementing composite writables.  It seems silly that we still don't have an equivalent in MR.
> I would like to see a new class with the following API:
> {code}
> package org.apache.hadoop.io;
> public class CompositeWritable<P extends WritableComparable, S extends WritableComparable> implements WritableComparable<CompositeWritable> {
>   public CompositeWritable(P primary, S secondary);
>   public P getPrimary();
>   public void setPrimary(P primary);
>   public S getSecondary();
>   public void setSecondary(S secondary);
>   // Return true if both primaries and both secondaries are equal
>   public boolean equals(CompositeWritable o);
>   // Return the primary's hash code
>   public long hashCode();
>   // Sort first by primary and then by secondary
>   public int compareTo(CompositeWritable o);
>   public void readFields(DataInput in);
>   public void write(DataOutput out);
> }
> {code}
> With such a class, implementing a secondary sort would mean just implementing a custom grouping comparator.  That comparator could also be implemented as part of this JIRA:
> {code}
> package org.apache.hadoop.io;
> public class CompositeGroupingComparator extends WritableComparator {
>   ...
> }
> {code}
> Or some such.
> Crunch also provides {{Tuple3}}, {{Tuple4}}, and {{TupleN}} classes, but I don't think we need to add equivalents.  If someone really wants that capability, they can nest composite keys.
> Don't forget to add unit tests!



--
This message was sent by Atlassian JIRA
(v6.3.4#6332)

---------------------------------------------------------------------
To unsubscribe, e-mail: mapreduce-issues-unsubscribe@hadoop.apache.org
For additional commands, e-mail: mapreduce-issues-help@hadoop.apache.org