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‎Changelog.rst‎

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@@ -9,6 +9,9 @@ Version NEXTVERSION
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* Allow multiple conditions for the same axis in `cf.Field.subspace`
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and `cf.Field.indices`
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(https://github.com/NCAS-CMS/cf-python/issues/881)
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* Fix bug in `cf.Field.collapse` that causes a ``ValueError`` to be raised
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for missing external cell measures data
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(https://github.com/NCAS-CMS/cf-python/issues/885)
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* Allow regridding for very large grids. New keyword parameter to
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`cf.Field.regrids` and `cf.Field.regridc`: ``dst_grid_partitions``
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(https://github.com/NCAS-CMS/cf-python/issues/878)

‎cf/field.py‎

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@@ -3689,7 +3689,12 @@ def weights(
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weights_axes.discard(xaxis)
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weights_axes.discard(yaxis)
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if not Weights.cell_measure(
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self, "area", comp, weights_axes, methods=methods
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self,
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"area",
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comp,
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weights_axes,
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methods=methods,
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auto=True,
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):
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Weights.area_XY(
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self,
@@ -5453,52 +5458,60 @@ def collapse(
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weights: optional
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Specify the weights for the collapse axes. The weights
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are, in general, those that would be returned by this
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call of the field construct's `weights` method:
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``f.weights(weights, axes=axes, measure=measure,
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scale=scale, radius=radius, great_circle=great_circle,
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components=True)``. See the *axes*, *measure*,
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*scale*, *radius* and *great_circle* parameters and
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`cf.Field.weights` for details, and note that the
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value of *scale* may be modified depending on the
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value of *measure*.
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are created internally as the output of this call of
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the field construct's `weights` method:
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``f.weights(weights, components=True, axes=axes,
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measure=measure, scale=scale, radius=radius,
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great_circle=great_circle)``.
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.. note:: By default *weights* is `None`, resulting in
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**unweighted calculations**.
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See the `cf.Field.weights` and the *axes*, *measure*,
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*scale*, *radius*, and *great_circle* parameters for
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details; and note that the value of *scale* may be
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modified depending on the value of *measure*.
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.. warning:: By default *weights* is `None`, resulting
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in **unweighted calculations**.
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.. note:: Setting *weights* to `True` is generally a
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good way to ensure that all collapses are
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appropriately weighted according to the
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field construct's metadata. In this case, if
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it is not possible to create weights for any
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axis then an exception will be raised.
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.. note:: Unless the *method* is ``'integral'``, the
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units of the weights are not combined with
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the field's units in the collapsed field.
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If the alternative form of providing the collapse method
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and axes combined as a CF cell methods-like string via the
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*method* parameter has been used, then the *axes*
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parameter is ignored and the axes are derived from the
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*method* parameter. For example, if *method* is ``'T:
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area: minimum'`` then this defines axes of ``['T',
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.. note:: A pre-calculated weights array or dictionary
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may also be provided as the *weights*
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parameter. See `cf.Field.weights` for
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details
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If the collapse method and axes have been provided as
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a CF cell methods-like string via the *method*
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parameter, then the *axes* parameter is ignored and
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the axes for weights instead inferred from that
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string. For instance, if *method* is ``'T: area:
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minimum'`` then this defines axes of ``['T',
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'area']``. If *method* specifies multiple collapses,
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e.g. ``'T: minimum area: mean'`` then this implies axes of
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``'T'`` for the first collapse, and axes of ``'area'`` for
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the second collapse.
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.. note:: Setting *weights* to `True` is generally a good
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way to ensure that all collapses are
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appropriately weighted according to the field
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construct's metadata. In this case, if it is not
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possible to create weights for any axis then an
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exception will be raised.
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However, care needs to be taken if *weights* is
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`True` when cell volume weights are desired. The
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volume weights will be taken from a "volume"
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cell measure construct if one exists, otherwise
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the cell volumes will be calculated as being
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proportional to the sizes of one-dimensional
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vertical coordinate cells. In the latter case
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**if the vertical dimension coordinates do not
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define the actual height or depth thickness of
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every cell in the domain then the weights will
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be incorrect**.
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e.g. ``'T: minimum area: mean'`` then this implies
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axes of ``'T'`` for the first collapse, and axes of
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``'area'`` for the second collapse.
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.. warning:: Care needs to be taken if *weights* is
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set to `True` when cell volume weights
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are desired. The volume weights will be
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taken from a "volume" cell measure
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construct if one exists, otherwise the
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cell volumes will be calculated as being
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proportional to the sizes of
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one-dimensional vertical coordinate
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cells. In the latter case **if the
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vertical dimension coordinates do not
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define the actual height or depth
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thickness of every cell in the domain
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then the weights will be incorrect**.
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*Parameter example:*
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To specify weights based on the field construct's

‎cf/weights.py‎

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@@ -1508,15 +1508,16 @@ def cell_measure(
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return False
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raise ValueError(
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f"Can't find weights: No {measure!r} cell measure"
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f"Can't find weights for {f!r}: No {measure!r} cell measure"
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)
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elif len_m > 1:
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if auto:
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return False
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raise ValueError(
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f"Can't find weights: Multiple {measure!r} cell measures"
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f"Can't find weights for {f!r}: Multiple {measure!r} cell "
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"measures"
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)
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key, clm = m.popitem()
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return False
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raise ValueError(
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f"Can't find weights: Cell measure {m!r} has no data, "
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"possibly because it is external. "
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"Consider setting cell_measures=False"
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f"Can't find weights for {f!r}: Cell measure {clm!r} has no "
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"data, possibly because it is in a missing external file. "
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"Consider setting cell_measures=False or, if applicable, "
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"re-reading the dataset whilst providing the external "
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"file (see cf.read for details)."
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)
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clm_axes0 = f.get_data_axes(key)
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return False
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raise ValueError(
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"Multiple weights specifications for "
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f"Can't find weights for {f!r}: Multiple weights "
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"specifications for "
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f"{f.constructs.domain_axis_identity(axis)!r} axis"
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)
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‎docs/source/contributing.rst‎

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@@ -124,6 +124,7 @@ ideas, code, and documentation to the cf library:
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* Mark Rhodes-Smith
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* Matt Brown
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* Michael Decker
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* Oliver Kotla
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* Sadie Bartholomew
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* Thibault Hallouin
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* Tim Bradshaw

‎docs/source/installation.rst‎

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@@ -117,6 +117,25 @@ Note that :ref:`some environment variables might also need setting
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<UNIDATA-UDUNITS-2-library>` in order for the Udunits library to work
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properly, although the defaults are usually sufficient.
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.. _Jupyter Notebooks:
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Jupyter Notebooks
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^^^^^^^^^^^^^^^^^
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You may want to work with cf via a Jupyter Notebook within a ``conda`` environment.
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A `known issue <https://github.com/NCAS-CMS/cf-python/issues/883/>`_ exists for Python 3.12 only when one wants to install the optional dependency ESMPy. Namely, the stricter dependencies of the Jupyter library clash with those of cf (namely ``zlib`` required by ESMPy) and installation fails.
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A proven workaround is to install Jupyter *before* installing cf, like so:
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.. code-block:: console
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:caption: *Install with conda alongside Jupyter.*
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$ conda install jupyter
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$ conda install -c conda-forge cf-python cf-plot udunits2
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$ conda install -c conda-forge "esmpy>=8.7.0"
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----
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.. _Source:

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