Merge pull request #3 from ufz/MergeDataArrays

Add another, more flexible script for merging data arrays.

post/merge-scalar-data-arrays/README.md

 # Merge two scalar data arrays
 
-This script takes two scalar nodal fields from a vtu file and combines them to a
+The script 'mergeDataArrays' takes two scalar nodal fields from a vtu file and combines them to a
 two-component vector field.
 
+The script 'mergeDataArraysIntoOne' takes arbitrary number of scalar fields from
+a vtu file and uses them as the components of a vector field that will be
+created.

post/merge-scalar-data-arrays/mergeDataArraysIntoOne.py

+#
+# \copyright
+# Copyright (c) 2012-2017, OpenGeoSys Community (http://www.opengeosys.org)
+#            Distributed under a Modified BSD License.
+#              See accompanying file LICENSE.txt or
+#              http://www.opengeosys.org/project/license
+#
+
+#!/usr/bin/env python2
+
+from vtk import *
+from sys import argv, exit
+
+if len(argv) < 5:
+    print "Usage:", argv[0], "input.vtu scalar_array1 ... name_for_new_array output.vtu"
+    exit(1)
+
+input_file = argv[1]
+output_file = argv[len(argv)-1]
+print("Reading from", input_file)
+print("Writing to", output_file)
+
+r = vtkXMLUnstructuredGridReader()
+r.SetFileName(input_file)
+r.Update()
+m = r.GetOutput()
+
+cell_data = m.GetCellData()
+tensor_arrays = []
+
+number_of_components = len(argv) - 4
+number_of_tuples = cell_data.GetArray(argv[(2)]).GetNumberOfTuples()
+
+for i in range(0, number_of_components):
+    tensor_arrays.append(cell_data.GetArray(argv[(i)+2]))
+
+new_array = vtkDoubleArray()
+new_array.SetNumberOfComponents(number_of_components)
+new_array.SetNumberOfTuples((number_of_tuples))
+new_array.SetName(argv[len(argv)-2])
+
+print "copy the particular cell data arrays to the cell data array ", argv[(len(argv)-2)]
+for i in range(0, number_of_components):
+    new_array.CopyComponent(i, tensor_arrays[i], 0)
+
+print "add ", argv[(len(argv)-2)], " to the data arrays"
+cell_data.AddArray(new_array)
+
+print "remove the not needed cell data arrays"
+
+for i in range(0, number_of_components):
+    print "remove the not needed cell data array", argv[(i)+2]
+    cell_data.RemoveArray(argv[(i)+2])
+
+print "write result to file"
+
+w = vtkXMLUnstructuredGridWriter()
+w.SetFileName(output_file)
+w.SetInputData(m)
+w.SetDataModeToAscii()
+w.SetCompressorTypeToNone()
+w.Update()