* Allowed invalid units through. Can test with `cf.Units.isvalid`.
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2.1.8
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**2018-03-08**
* Fixed bug when weights parameter is a string in `cf.Field.collapse`
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2.1.7
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**2018-02-13**
* Fixed bug in `cf.Field.collapse` when doing climatological time collapse with only one period per year/day
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2.1.6
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**2018-02-09**
* Fixed bug in Variable.mask
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2.1.4
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**2018-02-09**
* Added override_calendar method to coordinates and domain ancillaries that changes the calendar of the bounds, too. * Fixed bug in `cf.Data.where` when the condition is a `cf.Query` object. * Fixed bug in `cf.Variable.mask`
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2.1.3
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**2018-02-07**
* Allowed `scipy` and `matplotlib` imports to be optional