Composite Datasets

The pyvista.MultiBlock class is a composite class to hold many data sets which can be iterated over. MultiBlock behaves mostly like a list, but has some Dictionary-like features.

List-like Features

Create empty composite dataset

import pyvista as pv
from pyvista import examples
blocks = pv.MultiBlock()
blocks

Information	Blocks
MultiBlock Values N Blocks: 0 X Bounds: 0.000e+00, 0.000e+00 Y Bounds: 0.000e+00, 0.000e+00 Z Bounds: 0.000e+00, 0.000e+00	Index Name Type

Add some data to the collection.

blocks.append(pv.Sphere())
blocks.append(pv.Cube(center=(0, 0, -1)))

Plotting the MultiBlock plots all the meshes contained by it.

blocks.plot(smooth_shading=True)

MultiBlock is List-like, so individual blocks can be accessed via indices.

blocks[0]  # Sphere

Header	Data Arrays
PolyData Information N Cells 1680 N Points 842 N Strips 0 X Bounds -4.993e-01, 4.993e-01 Y Bounds -4.965e-01, 4.965e-01 Z Bounds -5.000e-01, 5.000e-01 N Arrays 1	Name Field Type N Comp Min Max Normals Points float32 3 -1.000e+00 1.000e+00

The length of the block can be accessed through len()

len(blocks)

2

or through the n_blocks attribute

blocks.n_blocks

2

More specifically, MultiBlock is a collections.abc.MutableSequence and supports operations such as append, pop, insert, etc. Some of these operations allow optional names to be provided for the dictionary like usage.

blocks.append(pv.Cone(), name="cone")
cone = blocks.pop(-1)  # Pops Cone
blocks.reverse()

MultiBlock also supports slicing for getting or setting blocks.

blocks[0:2]  # The Sphere and Cube objects in a new ``MultiBlock``

Information	Blocks
MultiBlock Values N Blocks: 2 X Bounds: -5.000e-01, 5.000e-01 Y Bounds: -5.000e-01, 5.000e-01 Z Bounds: -1.500e+00, 5.000e-01	Index Name Type 0 Block-01 PolyData 1 Block-00 PolyData

Dictionary-like Features

MultiBlock also has some dictionary features. We can set the name of the blocks, and then access them

blocks = pv.MultiBlock([pv.Sphere(), pv.Cube()])
blocks.set_block_name(0, "sphere")
blocks.set_block_name(1, "cube")
blocks["sphere"]  # Sphere

Header	Data Arrays
PolyData Information N Cells 1680 N Points 842 N Strips 0 X Bounds -4.993e-01, 4.993e-01 Y Bounds -4.965e-01, 4.965e-01 Z Bounds -5.000e-01, 5.000e-01 N Arrays 1	Name Field Type N Comp Min Max Normals Points float32 3 -1.000e+00 1.000e+00

It is important to note that MultiBlock is not a dictionary and does not enforce unique keys. Keys can also be None. Extra care must be taken to avoid problems using the Dictionary-like features.

PyVista tries to keep the keys ordered correctly when doing list operations.

blocks.reverse()
blocks.keys()

['cube', 'sphere']

The dictionary like features are useful when reading in data from a file. The keys are often more understandable to access the data than the index. pyvista.examples.download_cavity() is an OpenFoam dataset with a nested MultiBlock structure. There are two entries in the top-level object

data = examples.download_cavity()
data.keys()

['internalMesh', 'boundary']

"internalMesh" is a pyvista.UnstructuredGrid.

data["internalMesh"]

Header	Data Arrays
UnstructuredGrid Information N Cells 400 N Points 882 X Bounds 0.000e+00, 1.000e-01 Y Bounds 0.000e+00, 1.000e-01 Z Bounds 0.000e+00, 1.000e-02 N Arrays 4	Name Field Type N Comp Min Max U Points float32 3 0.000e+00 1.000e+00 p Points float32 1 0.000e+00 0.000e+00 U Cells float32 3 0.000e+00 0.000e+00 p Cells float32 1 0.000e+00 0.000e+00

"boundary" is another pyvista.MultiBlock.

data["boundary"]

Information	Blocks
MultiBlock Values N Blocks: 3 X Bounds: 0.000e+00, 1.000e-01 Y Bounds: 0.000e+00, 1.000e-01 Z Bounds: 0.000e+00, 1.000e-02	Index Name Type 0 movingWall PolyData 1 fixedWalls PolyData 2 frontAndBack PolyData

Using the dictionary like features of pyvista.MultiBlock allow for easier inspection and use of the data coming from an outside source. The names of each key correspond to human understandable portions of the dataset.

data["boundary"].keys()

['movingWall', 'fixedWalls', 'frontAndBack']

Examples using this class:

• Slicing

• Volumetric Analysis

• Depth Peeling

MultiBlock API Reference

The pyvista.MultiBlock class holds attributes that are common to all spatially referenced datasets in PyVista. This base class is analogous to VTK’s vtk.vtkMultiBlockDataSet class.

pyvista.MultiBlock(*args, **kwargs)

A composite class to hold many data sets which can be iterated over.