# Modify values from grouped rows

Use the Modify values from grouped rows step to build complex hierarchical data and group data based on a hierarchical data field using path definitions on an ordered group of input rows. This step modifies hierarchical data to form nested JSON key-value pairs. It can also build complex data by nesting arrays, objects, and key-value pairs. The step takes non-hierarchical data and changes it to hierarchical data and sends it to other steps. See [Hierarchical data](/pdia-data-integration/10.2-data-integration/advanced-topics-pentaho-data-integration-overview/hierarchical-data.md) for an overview of hierarchical data in Pentaho.


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