GetInputArray(
int idx, vtkDataObject* data, int association);
```
The latter methods would return either a smart pointer to the original array (if it had an acceptable number of components) or a smart pointer to a `vtkImplicitArray` that extracts the given component or norm from an original multi-component array as requested by the caller to `SetInputArrayToProcess()`.
---
### Author:  [@dcthomp](https://discourse.vtk.org/u/dcthomp)
#### Post date: [August 14, 2025, 12:00pm UTC](https://discourse.vtk.org/t/proposal-add-array-component-to-vtkalgorithm-setinputarraytoprocess/15964/2 "2025-08-14T12:00:08Z")
@berk.geveci @mwestphal I believe you will both have opinions about this. 🙂
---
### Author:  [@berk.geveci](https://discourse.vtk.org/u/berk.geveci)
#### Post date: [August 14, 2025, 1:54pm UTC](https://discourse.vtk.org/t/proposal-add-array-component-to-vtkalgorithm-setinputarraytoprocess/15964/3 "2025-08-14T13:54:58Z")
> I would also like to add a method to create a procedural single-component array (using `vtkImplicitArray` ) on demand that holds the single component specified (in cases where the array has multiple components).
I don’t understand what this means.
---
### Author:  [@berk.geveci](https://discourse.vtk.org/u/berk.geveci)
#### Post date: [August 14, 2025, 2:02pm UTC](https://discourse.vtk.org/t/proposal-add-array-component-to-vtkalgorithm-setinputarraytoprocess/15964/4 "2025-08-14T14:02:02Z")
The concept is reasonable. I don’t love the idea of adding yet new GetInputArray() methods when there are already 6 of them. I understand the need for backwards compatibility but I still don’t like it. I also don’t love the fact that a Get method can return a newly allocated array. It is not the norm for VTK (except for lazy evaluation where someone else still holds the pointer). ParaView handles this use case in the UI, doesn’t it? There is some kind of upstream magic filter that does this somehow? If this is for VTK only, maybe it is fine for people to apply a filter for the extraction?
---
### Author:  [@dcthomp](https://discourse.vtk.org/u/dcthomp)
#### Post date: [August 14, 2025, 2:37pm UTC](https://discourse.vtk.org/t/proposal-add-array-component-to-vtkalgorithm-setinputarraytoprocess/15964/5 "2025-08-14T14:37:34Z")
> [@berk.geveci](#):
>
> I also don’t love the fact that a Get method can return a newly allocated array. It is not the norm for VTK (except for lazy evaluation where someone else still holds the pointer)
The idea was that `GetInputArray()` would be called inside `RequestData()` and then discarded. The smart-pointer it returned would either be (a) already owned by the input data object or (b) a very small `vtkImplicitArray` that adapts an array already owned by the input data object.
> [@berk.geveci](#):
>
> ParaView handles this use case in the UI, doesn’t it?
Not that I’m aware of. All the filters that require a single component provide both an array-selector (i.e., a `vtkSMArrayListDomain` on a string property and a separate integer property that lets you choose a component). But that only works for 1 array/component-pair at a time.
My plan for ParaView was to add a `vtkSMArrayComponentSelectionDomain` whose property-helper would be aware of how to call the new method. There would be a `pqArrayComponentSelector` that the statistics algorithms (and others) could use to select any number of components of different arrays of interest. For example, if you want to compute correlations between X acceleration and each component of strain tensor, you would be allowed to do that. Or correlate X acceleration to Y acceleration.
---
### Author:  [@dcthomp](https://discourse.vtk.org/u/dcthomp)
#### Post date: [August 14, 2025, 2:40pm UTC](https://discourse.vtk.org/t/proposal-add-array-component-to-vtkalgorithm-setinputarraytoprocess/15964/6 "2025-08-14T14:40:56Z")
> [@berk.geveci](#):
>
> I don’t understand what this means.
The `vtkImplicitArray` class makes it easy to take an existing N-component array and return a single-component array that procedurally just fetches the i-th component for any given tuple. It owns a reference to the N-component array. So filters could just use that array internally as if the user had extracted the component of interest. There is a small time-overhead, but no space overhead – and if users care about speed, they can add calculator filters to the pipeline to extract components they care about.
---
### Author:  [@berk.geveci](https://discourse.vtk.org/u/berk.geveci)
#### Post date: [August 14, 2025, 3:17pm UTC](https://discourse.vtk.org/t/proposal-add-array-component-to-vtkalgorithm-setinputarraytoprocess/15964/7 "2025-08-14T15:17:51Z")
> The `vtkImplicitArray` class makes it easy to take an existing N-component array and return a single-component array that procedurally just fetches the i-th component for any given tuple. It owns a reference to the N-component array. So filters could just use that array internally as if the user had extracted the component of interest. There is a small time-overhead, but no space overhead – and if users care about speed, they can add calculator filters to the pipeline to extract components they care about.
Got it. It is useful to have this irrespective of the rest of the conversation.
---
### Author:  [@berk.geveci](https://discourse.vtk.org/u/berk.geveci)
#### Post date: [August 14, 2025, 3:19pm UTC](https://discourse.vtk.org/t/proposal-add-array-component-to-vtkalgorithm-setinputarraytoprocess/15964/8 "2025-08-14T15:19:54Z")
> [@dcthomp](#):
>
> Not that I’m aware of. All the filters that require a single component provide both an array-selector (i.e., a `vtkSMArrayListDomain` on a string property and a separate integer property that lets you choose a component). But that only works for 1 array/component-pair at a time.
If I turn on “Auto convert properties” in the settings and then try to contour a dataset with vectors in it, I see all the components of the vectors (with \_X, \_Y, \_Z names) and the magnitude in the list. Isn’t this what we are talking about? Try: Wavelet → Random Vectors → Contour after turning on the “auto convert properties” option.
---
### Author:  [@dcthomp](https://discourse.vtk.org/u/dcthomp)
#### Post date: [August 14, 2025, 4:52pm UTC](https://discourse.vtk.org/t/proposal-add-array-component-to-vtkalgorithm-setinputarraytoprocess/15964/9 "2025-08-14T16:52:10Z")
> [@berk.geveci](#):
>
> If I turn on “Auto convert properties” in the settings and then try to contour a dataset with vectors in it, I see all the components of the vectors (with \_X, \_Y, \_Z names) and the magnitude in the list. Isn’t this what we are talking about?
I thought auto-convert only did cell↔point conversion. I agree, with auto-conversion forced, there is no need for a new domain.
---
### Author:  [@cory.quammen](https://discourse.vtk.org/u/cory.quammen)
#### Post date: [August 14, 2025, 5:05pm UTC](https://discourse.vtk.org/t/proposal-add-array-component-to-vtkalgorithm-setinputarraytoprocess/15964/10 "2025-08-14T17:05:23Z")
Auto-convert properties in ParaView works by putting a ParaView-specific `vtkPVPostFilter` in the pipeline to expose the different components and do the point-to-cell and cell-to-point data conversio.
---
### Author:  [@dcthomp](https://discourse.vtk.org/u/dcthomp)
#### Post date: [August 23, 2025, 4:11am UTC](https://discourse.vtk.org/t/proposal-add-array-component-to-vtkalgorithm-setinputarraytoprocess/15964/11 "2025-08-23T04:11:49Z")
One issue that creates is that the statistics filters in VTK will not be able to benefit from it (aside from ParaView). Which makes adding the methods above relevant even if ParaView does not use them.
There is a [VTK merge request](https://gitlab.kitware.com/vtk/vtk/-/merge_requests/12387) that implements the implicit array backends, component-selection API, and a free function `vtk::ComponentOrNormAsArray()`.