improver.utilities.indexing_operations module

Module to contain indexing operation functions.

choose(index_array, array_set)

Create a reordered copy of a data array, where an index array of matching shape determines how the data is reordered.

The reordered copy of the array will have the same shape as the inputs. If a 3-dimensional array_set is provided, the data coordinates could be described as A[i, j, k]. This function does not rearrange the j and k coordinates. The reordered array is constructed by substituting into each position [i, j, k] in the index_array a value taken from the array_set at a matching [j, k] position, but where [i] is determined by the given index value. As such the index values must run 0 - N-1 where N is the length of the leading dimension of array_set (and equivalently of index_array).

The following figure gives an examples of the expected result of this function for a given index_array and array_set.

The input data array is reordered along the leading dimension (i), but maintains its sub-array position (j, k), denoted here by the different colours.

Parameters:

• index_array (ndarray) – This array must contain integers in the range [0, N-1], where N is if the length of the leading dimension of the array_set array. These integers determine how array_set will be reordered in the returned array.

• array_set (ndarray) – A multi-dimensional array, where the leading dimension is in effect an indexing dimension. Within this leading dimension are the sub-arrays from which values are to be extracted at positions that match those given in the index_array.

Return type:

ndarray

Returns:

An array containing the reordered data extracted from array_set. The returned array will have the same shape as the index_array and array_set arrays.

Raises:

• ValueError – If index_array and array_set do not have matching shapes.

• IndexError – If an index exceeds the length of the leading dimension of the array_set array (N-1).