# Catalyst2 and grouping output
**URL:** https://discourse.paraview.org/t/catalyst2-and-grouping-output/13224
**Category:** In Situ Support
**Tags:** catalyst
**Created:** [November 9, 2023, 10:26pm UTC](https://discourse.paraview.org/t/catalyst2-and-grouping-output/13224 "2023-11-09T22:26:47Z")
**Posts on this page:** 4
**Page:** 1
### Author:  [@zetwal](https://discourse.paraview.org/u/zetwal)
#### Post date: [November 9, 2023, 10:26pm UTC](https://discourse.paraview.org/t/catalyst2-and-grouping-output/13224/1 "2023-11-09T22:26:47Z")
Hello
I’m using the [gridwriter.py sample script](https://gitlab.kitware.com/paraview/paraview/-/blob/v5.11.2/Examples/Catalyst2/SampleScripts/gridwriter.py?ref_type=tags) to write data out from Catalyst. The issue is as the number of ranks increases, the number of output files also goes up. Is there a way to group data from several ranks to output fewer files, and thus reduce writing out time?
Thanks
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### Author:  [@boonth](https://discourse.paraview.org/u/boonth)
#### Post date: [November 9, 2023, 11:40pm UTC](https://discourse.paraview.org/t/catalyst2-and-grouping-output/13224/2 "2023-11-09T23:40:35Z")
Hi Pascal,
You can use the `AggregateDataset` filter for this.
```
aggregateDataset1 = AggregateDataset(Input=grid)
aggregateDataset1.NumberOfTargetProcesses = 8
```
The `NumberOfTargetProcesses` is the number of ranks that will write out files.
---
### Author:  [@zetwal](https://discourse.paraview.org/u/zetwal)
#### Post date: [November 10, 2023, 2:46pm UTC](https://discourse.paraview.org/t/catalyst2-and-grouping-output/13224/3 "2023-11-10T14:46:09Z")
Hi Boonth
Do you just put that in the gridWriter script?
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### Author:  [@boonth](https://discourse.paraview.org/u/boonth)
#### Post date: [November 10, 2023, 4:36pm UTC](https://discourse.paraview.org/t/catalyst2-and-grouping-output/13224/4 "2023-11-10T16:36:59Z")
No, I took that from another Catalyst 1.0 script. You’ll have to adapt it to your script.
Boonth