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DOC: Note about collapsing multi-dimensional coordinates #1819

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Nov 23, 2015
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DOC: Note about collapsing multi-dimensional coordinates #1819

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f1331b5
Multi-dimensional coordinate collapse note
DPeterK Oct 28, 2015
53a6795
Review actions: move new docs around.
DPeterK Nov 23, 2015
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3 changes: 3 additions & 0 deletions docs/iris/src/userguide/cube_statistics.rst
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Expand Up @@ -97,6 +97,9 @@ For an example of using this functionality, the
in the gallery takes a zonal mean of an ``XYT`` cube by using the
``collapsed`` method with ``latitude`` and ``iris.analysis.MEAN`` as arguments.

You cannot partially collapse a multi-dimensional coordinate. See
:ref:`cube.collapsed <partially_collapse_multi-dim_coord>` for more
information.

.. _cube-statistics-collapsing-average:

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7 changes: 6 additions & 1 deletion lib/iris/coords.py
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Expand Up @@ -943,11 +943,16 @@ def cell(self, index):

def collapsed(self, dims_to_collapse=None):
"""
Returns a copy of this coordinate which has been collapsed along
Returns a copy of this coordinate, which has been collapsed along
the specified dimensions.

Replaces the points & bounds with a simple bounded region.

.. note::
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I'm not sure this note is well targeted for coordinates.

You cannot partially collapse a multi-dimensional coordinate. See
:ref:`cube.collapsed <partially_collapse_multi-dim_coord>` for more
information.

"""
if isinstance(dims_to_collapse, (int, np.integer)):
dims_to_collapse = [dims_to_collapse]
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15 changes: 15 additions & 0 deletions lib/iris/cube.py
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Expand Up @@ -2945,6 +2945,21 @@ def collapsed(self, coords, aggregator, **kwargs):
cube.collapsed(['latitude', 'longitude'],
iris.analysis.VARIANCE)

.. _partially_collapse_multi-dim_coord:

.. note::
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👍 for more detail in here which we can cross reference.

You cannot partially collapse a multi-dimensional coordinate. Doing
so would result in a partial collapse of the multi-dimensional
coordinate. Instead you must either:
* collapse in a single operation all cube axes that the
multi-dimensional coordinate spans,
* remove the multi-dimensional coordinate from the cube before
performing the collapse operation, or
* not collapse the coordinate at all.

Multi-dimensional derived coordinates will not prevent a successful
collapse operation.

"""
# Convert any coordinate names to coordinates
coords = self._as_list_of_coords(coords)
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