Resolve "make friendly example scripts for the release"

Closes #626 (closed)

python/corsika/io/converters/arrow_to_numpy.py

+"""
+ Converter for the pyarrow data types to numpy ones
+
+ (c) Copyright 2020 CORSIKA Project, corsika-project@lists.kit.edu
+
+ This software is distributed under the terms of the GNU General Public
+ Licence version 3 (GPL Version 3). See file LICENSE for a full version of
+ the license.
+"""
+
+import pyarrow
+import numpy as np
+
+def convert_to_numpy(pyarrow_table: pyarrow.lib.Table) -> np.ndarray:
+    """
+    Converts a pyarrow Table to a numpy structured array
+
+    Parameters
+    ----------
+    pyarrow_table: pyarrow.lib.Table
+        PyArrow table of any dimension to be sliced
+
+    Returns
+    -------
+    np.ndarray:
+        converted table with the same column labels and data types
+
+    """
+
+    # Type conversions for pyarrow data types to numpy ones
+    # pyarrow: https://arrow.apache.org/docs/python/data.html
+    # numpy: https://numpy.org/doc/stable/reference/arrays.dtypes.html#arrays-dtypes-constructing
+    type_conversions = {
+        pyarrow.int8(): "int8",
+        pyarrow.int16(): "int16",
+        pyarrow.int32(): "int32",
+        pyarrow.int64(): "int64",
+        pyarrow.uint8(): "uint8",
+        pyarrow.uint16(): "uint16",
+        pyarrow.uint32(): "uint32",
+        pyarrow.uint64(): "uint64",
+        pyarrow.float16(): "float16",
+        pyarrow.float32(): "float32",
+        pyarrow.float64(): "float64",
+    }
+
+    # Perform type conversion of all fields
+    column_types = [type_conversions[pyarrow_table[key].type] for key in pyarrow_table.column_names]
+
+    # Make an empty array and then fill the values
+    np_table = np.zeros(pyarrow_table.num_rows, dtype={"names": pyarrow_table.column_names, "formats": column_types})
+    for key in pyarrow_table.column_names:
+        np_table[key] = pyarrow_table[key]
+
+    return np_table