# Operations on multi-block dataset with Programmable Filter

**URL:** https://discourse.paraview.org/t/operations-on-multi-block-dataset-with-programmable-filter/1027
**Category:** ParaView Support
**Created:** [December 11, 2018, 9:18am UTC](https://discourse.paraview.org/t/operations-on-multi-block-dataset-with-programmable-filter/1027 "2018-12-11T09:18:07Z")
**Posts on this page:** 1
**Showing post:** 6

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### Author: ![cory.quammen](https://discourse.paraview.org/user_avatar/discourse.paraview.org/cory.quammen/32/11193_2.png) [@cory.quammen](https://discourse.paraview.org/u/cory.quammen)
#### Post date: [December 11, 2018, 6:29pm UTC](https://discourse.paraview.org/t/operations-on-multi-block-dataset-with-programmable-filter/1027/6 "2018-12-11T18:29:20Z")

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> [@pcrepier](#):
>
> So there seem to be something going on with multi-block datasets.

Ah, indeed. The usual numpy functions do not work for `VTKCompositeDataArrays` that are available from multiblock datasets, but the numpy-like algorithms provided by `vtk.numpy_interface.algorithms` do. However, the `where` function provided in `vtk.numpy_interface.algorithms` is only the single-argument version, not the three-argument version I suggested, so merging the blocks is the only way to use this numpy expression currently.

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