zvalue_from_index for KRSTN

zvalue_from_index.py

def _zvalue_from_index(arr, ind):
	"""private helper function to work around the limitation of np.choose() by employing np.take()
	arr has to be a 3D array
	ind has to be a 2D array containing values for z-indicies to take from arr
	See: http://stackoverflow.com/a/32091712/4169585
	This is faster and more memory efficient than using the ogrid based solution with fancy indexing.
	"""
	
	# get number of rows and columns
	_,nR,nC = arr.shape
	
	# get linear indices and extract elements with np.take()
	idx = nC*nR*ind + nC*np.arange(nR)[:,None] + np.arange(nC)
	return np.take(arr, idx)