def cube_delta(cube, coord):
"""
Given a cube calculate the difference between each value in the given coord's direction.
Args:
* coord
either a Coord instance or the unique name of a coordinate in the cube.
If a Coord instance is provided, it does not necessarily have to exist in the cube.
Example usage::
change_in_temperature_wrt_pressure = cube_delta(temperature_cube, 'pressure')
.. note:: Missing data support not yet implemented.
"""
# handle the case where a user passes a coordinate name
if isinstance(coord, basestring):
coord = cube.coord(coord)
if coord.ndim != 1:
raise iris.exceptions.CoordinateMultiDimError(coord)
# Try and get a coord dim
delta_dims = cube.coord_dims(coord)
if (coord.shape[0] == 1
and not getattr(coord, 'circular', False)) or not delta_dims:
raise ValueError(
'Cannot calculate delta over "%s" as it has length of 1.' %
coord.name())
delta_dim = delta_dims[0]
# Calculate the actual delta, taking into account whether the given coordinate is circular
delta_cube_data = delta(cube.data,
delta_dim,
circular=getattr(coord, 'circular', False))
# If the coord/dim is circular there is no change in cube shape
if getattr(coord, 'circular', False):
delta_cube = cube.copy(data=delta_cube_data)
else:
# Subset the cube to the appropriate new shape by knocking off the last row of the delta dimension
subset_slice = [slice(None, None)] * cube.ndim
subset_slice[delta_dim] = slice(None, -1)
delta_cube = cube[tuple(subset_slice)]
delta_cube.data = delta_cube_data
# Replace the delta_dim coords with midpoints (no shape change if circular).
for cube_coord in cube.coords(dimensions=delta_dim):
delta_cube.replace_coord(
_construct_midpoint_coord(cube_coord,
circular=getattr(coord, 'circular',
False)))
delta_cube.rename('change_in_%s_wrt_%s' %
(delta_cube.name(), coord.name()))
return delta_cube
def cube_delta(cube, coord):
"""
Given a cube calculate the difference between each value in the
given coord's direction.
Args:
* coord
either a Coord instance or the unique name of a coordinate in the cube.
If a Coord instance is provided, it does not necessarily have to
exist in the cube.
Example usage::
change_in_temperature_wrt_pressure = \
cube_delta(temperature_cube, 'pressure')
.. note:: Missing data support not yet implemented.
"""
# handle the case where a user passes a coordinate name
if isinstance(coord, six.string_types):
coord = cube.coord(coord)
if coord.ndim != 1:
raise iris.exceptions.CoordinateMultiDimError(coord)
# Try and get a coord dim
delta_dims = cube.coord_dims(coord.name())
if (coord.shape[0] == 1 and not getattr(coord, "circular", False)) or not delta_dims:
raise ValueError("Cannot calculate delta over {!r} as it has " "length of 1.".format(coord.name()))
delta_dim = delta_dims[0]
# Calculate the actual delta, taking into account whether the given
# coordinate is circular.
delta_cube_data = delta(cube.data, delta_dim, circular=getattr(coord, "circular", False))
# If the coord/dim is circular there is no change in cube shape
if getattr(coord, "circular", False):
delta_cube = cube.copy(data=delta_cube_data)
else:
# Subset the cube to the appropriate new shape by knocking off
# the last row of the delta dimension.
subset_slice = [slice(None, None)] * cube.ndim
subset_slice[delta_dim] = slice(None, -1)
delta_cube = cube[tuple(subset_slice)]
delta_cube.data = delta_cube_data
# Replace the delta_dim coords with midpoints
# (no shape change if circular).
for cube_coord in cube.coords(dimensions=delta_dim):
delta_cube.replace_coord(_construct_midpoint_coord(cube_coord, circular=getattr(coord, "circular", False)))
delta_cube.rename("change_in_{}_wrt_{}".format(delta_cube.name(), coord.name()))
return delta_cube