# Change values of array of selected elements

**URL:** https://discourse.paraview.org/t/change-values-of-array-of-selected-elements/16644
**Category:** Development
**Tags:** python
**Created:** [May 17, 2025, 4:09pm UTC](https://discourse.paraview.org/t/change-values-of-array-of-selected-elements/16644 "2025-05-17T16:09:07Z")
**Posts on this page:** 2
**Page:** 1

<div class="post-metadata">

### Author: ![Clockwork](https://discourse.paraview.org/user_avatar/discourse.paraview.org/clockwork/32/8251_2.png) [@Clockwork](https://discourse.paraview.org/u/Clockwork)
#### Post date: [May 17, 2025, 4:09pm UTC](https://discourse.paraview.org/t/change-values-of-array-of-selected-elements/16644/1 "2025-05-17T16:09:07Z")

</div>

I have a method of selecting cells and changing the values in that portion of the array to a new integer, but it is quite cumbersome. So, for example, I might have a mesh that has a “Region” cell array with all integer 1 values. I want to select a portion of this and give that selected portion of the “Region” cell array value 2 (or some other pre-defined user integer value).

I’m hoping that either there is a better way in general, or since this method was created a decade ago, that new features may be able to improve this workflow. Currently, I am using two programmable filters to accomplish this. The first is to give each a global ID for when I split up the mesh:

```auto
input = self.GetInputDataObject(0,0)
output = self.GetOutputDataObject(0)
numCells = input.GetNumberOfCells()

globalIds = vtk.vtkDoubleArray()
globalIds.SetNumberOfValues(numCells)
globalIds.SetName("GlobalIds")

origMats = input.GetCellData().GetArray("Region")

matIds = vtk.vtkDoubleArray()
matIds.SetNumberOfValues(numCells)
matIds.SetName("Region")

for ii in range(numCells):
	globalIds.InsertValue(ii,ii)
	matIds.InsertValue(ii, int(origMats.GetTuple1(ii)))

output.GetCellData().AddArray(globalIds)
output.GetCellData().AddArray(matIds)

```

I then have to select a region, then extract that region, and then select that new region plus the original regionIds, and use the next custom filter to change the material:

```auto

#Changes material of selected region to 
#the value set here
matID = 2

#Just in case this needs to be done on 
#data formatted differently
array = 'Region'

####################################

def getSelection(sel, obj):
	currentCell = vtk.vtkGenericCell()
	oldPts = sel.GetCellData().GetArray("GlobalIds")
	pointsToChange = []

	for ii in range(sel.GetNumberOfCells()):
		pointsToChange.append(int(oldPts.GetTuple1(ii)))
	
	return pointsToChange

inp1 = self.GetInputDataObject(0,0)
inp2 = self.GetInputDataObject(0,1)
output = self.GetOutputDataObject(0)

num1 = inp1.GetNumberOfCells()
num2 = inp2.GetNumberOfCells()

if num1 > num2:
	toChange= getSelection(inp2, inp1)
	output.DeepCopy(inp1)

else:
	toChange= getSelection(inp1, inp2)
	output.DeepCopy(inp2)
	
oldIds = output.GetCellData().GetArray(array)
for ii in toChange:
	oldIds.SetComponent(ii, 0, float(matID))

```

As I previously stated, this can become quite cumbersome when it’s necessary to do it over and over. Are there any potential ways to speed up or streamline this workflow?

Thanks!

---

<div class="post-metadata">

### 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: [May 19, 2025, 6:34pm UTC](https://discourse.paraview.org/t/change-values-of-array-of-selected-elements/16644/2 "2025-05-19T18:34:17Z")

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The **Global Point and Cell IDs** filter should at least take care of doing what your first **Programmable Filter** does.

I can’t think of a filter that applies data to a selection as you are doing in the second one, though. There is **Annotate Selection** , but that produces a new string array with values rather than an integer array.