docs/apis/zip_elements_guide.md

---
title: "Zipping Elements in a DataSet"
---
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In certain algorithms, one may need to assign unique identifiers to data set elements.
This document shows how {% gh_link /flink-java/src/main/java/org/apache/flink/api/java/utils/DataSetUtils.java "DataSetUtils" %} can be used for that purpose.

* This will be replaced by the TOC
{:toc}

### Zip with a Dense Index
For assigning consecutive labels to the elements, the `zipWithIndex` method should be called. It receives a data set as input and returns a new data set of unique id, initial value tuples.
For example, the following code:

<div class="codetabs" markdown="1">
<div data-lang="java" markdown="1">
{% highlight java %}
ExecutionEnvironment env = ExecutionEnvironment.getExecutionEnvironment();
env.setParallelism(1);
DataSet<String> in = env.fromElements("A", "B", "C", "D", "E", "F");

DataSet<Tuple2<Long, String>> result = DataSetUtils.zipWithIndex(in);

result.writeAsCsv(resultPath, "\n", ",");
env.execute();
{% endhighlight %}
</div>

<div data-lang="scala" markdown="1">
{% highlight scala %}
import org.apache.flink.api.scala._

val env: ExecutionEnvironment = ExecutionEnvironment.getExecutionEnvironment
env.setParallelism(1)
val input: DataSet[String] = env.fromElements("A", "B", "C", "D", "E", "F")

val result: DataSet[(Long, String)] = input.zipWithIndex

result.writeAsCsv(resultPath, "\n", ",")
env.execute()
{% endhighlight %}
</div>

</div>

will yield the tuples: (0,A), (1,B), (2,C), (3,D), (4,E), (5,F)

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### Zip with an Unique Identifier
In many cases, one may not need to assign consecutive labels.
`zipWIthUniqueId` works in a pipelined fashion, speeding up the label assignment process. This method receives a data set as input and returns a new data set of unique id, initial value tuples.
For example, the following code:

<div class="codetabs" markdown="1">
<div data-lang="java" markdown="1">
{% highlight java %}
ExecutionEnvironment env = ExecutionEnvironment.getExecutionEnvironment();
env.setParallelism(1);
DataSet<String> in = env.fromElements("A", "B", "C", "D", "E", "F");

DataSet<Tuple2<Long, String>> result = DataSetUtils.zipWithUniqueId(in);

result.writeAsCsv(resultPath, "\n", ",");
env.execute();
{% endhighlight %}
</div>

<div data-lang="scala" markdown="1">
{% highlight scala %}
import org.apache.flink.api.scala._

val env: ExecutionEnvironment = ExecutionEnvironment.getExecutionEnvironment
env.setParallelism(1)
val input: DataSet[String] = env.fromElements("A", "B", "C", "D", "E", "F")

val result: DataSet[(Long, String)] = input.zipWithUniqueId

result.writeAsCsv(resultPath, "\n", ",")
env.execute()
{% endhighlight %}
</div>

</div>

will yield the tuples: (0,A), (2,B), (4,C), (6,D), (8,E), (10,F)

[Back to top](#top)