Top-N returns the top "n" records from the input set, based on the criteria specified in the plugin configuration.
| Config | Required | Default | Description |
|---|---|---|---|
| Top Field | Y | n/a | Input field that should be used to compare records. It must be a numeric type (int, long, float, or double). |
| Results Number | N | 1 | Specifies the size of the top-N to be generated. If the number of input records is less than N, then all records will be ordered by the Top Field specified above. |
| Ignore NULL Value | N | false |
Whether to ignore records with a NULL value in the Top Field. Defaults to false to treat NULL as the smallest value. |
This plugin takes input records and returns a specified number of records with the highest values in a given field. If the total number of input records is smaller than the specifed number, output records will contain all records sorted by their values in the given field in a descending order.
Here is how the plugin works with a simple example. Let's say the input records have two columns ("name" and "age") and you want to track the top three records, ordered by "age", without ignoring null values. The configuration for the plugin would specify:
- Top Field as
age - Results Number as
3 - Ignore NULL Value as
false
If these are the input records:
+================+
| name | age |
+================+
| alice | NULL |
| bob | 1 |
| dave | 6 |
+================+
then after applying the configuration, the output records will be:
+================+
| name | age |
+================+
| dave | 6 |
| bob | 1 |
| alice | NULL |
+================+
If the Null Field Value is set to true to ignore records with NULL values in the "age" field, the output records will be:
+================+
| name | age |
+================+
| dave | 6 |
| bob | 1 |
+================+
To build this plugin:
git clone https://github.com/hydrator/topn.git
mvn clean package
The build will create a .jar and .json files under the target directory.
These files are used to deploy your plugins.
You can deploy your plugins using the CDAP CLI:
> load artifact <target/topn-<version>.jar> config-file <target/topn-<version>.json>
For example, if your artifact is named 'topn-':
> load artifact target/topn-<version>.jar config-file target/topn-<version>.json
CDAP User Group and Development Discussions:
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CDAP IRC Channel: #cdap on irc.freenode.net
Copyright © 2017 Cask Data, Inc.
Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License. You may obtain a copy of the License at
http://www.apache.org/licenses/LICENSE-2.0
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