# Memory Group By

The **Memory Group By** step groups rows in memory from a source step. The resulting rows are grouped based on a specified field or collection of fields. A new row is generated for each group.

This step differs from the [Group By](/pdia-data-integration/pdi-transformation-steps-reference-overview/group-by-landing-page-article.md) step by processing all rows in memory and by handling non-sorted input.

If the number of rows you want to group is too large to fit into memory, use a combination of [Sort rows](/pdia-data-integration/pdi-transformation-steps-reference-overview/sort-rows-transformation-step.md) and Group By.

### General

| Option                            | Definition                                                                                                                 |
| --------------------------------- | -------------------------------------------------------------------------------------------------------------------------- |
| **Step name**                     | Specify the unique name of the Memory Group By step on the canvas. You can customize the name or leave it as the default.  |
| **Always give back a result row** | Select to return a result row even when there is no input row. If no input rows exist, this option returns a count of `0`. |

![Memory Group By dialog](/files/NJXyph3NYjvt3uI8w9Ro)

### Group fields

Use this table to specify the fields you want to group.

* Select **Get fields** to add all fields from the incoming stream.
* Leave this table blank to calculate aggregate functions over the entire dataset.

### Aggregates

Use this table to specify the aggregation method and the name of the resulting field.

| Column      | Description                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  |
| ----------- | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------ |
| **Name**    | The name of the aggregate field.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             |
| **Subject** | The subject on which you want to use an aggregation method.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  |
| **Type**    | <p>The aggregation method. Available methods include:</p><ul><li>Sum</li><li>Average (Mean)</li><li>Median</li><li>Percentile</li><li>Minimum</li><li>Maximum</li><li>Number of values (N)</li><li>Concatenate strings separated by , (comma)</li><li>First non-null value</li><li>Last non-null value</li><li>First value (including null)</li><li>Last value (including null)</li><li>Standard deviation</li><li>Concatenate strings separated by the character specified in the <strong>Value</strong> column</li><li>Number of distinct values</li><li>Number of rows (without field argument)</li></ul> |
| **Value**   | The aggregate value.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         |

### Metadata injection support

This step supports metadata injection. You can use it with [ETL metadata injection](/pdia-data-integration/pdi-transformation-steps-reference-overview/etl-metadata-injection.md) to pass metadata to your transformation at runtime.


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