cf.Field.subspace

Field.subspace

Return a new object which in turn may return a subspace of the field.

The subspace attribute may be indexed to select a subspace by dimension index values (f.subspace[indices]) or called to select a subspace by dimension coordinate array values (f.subpace(**coordinate_values)).

Subspacing by indexing

Subspacing by dimension indices uses an extended Python slicing syntax, which is similar numpy array indexing

There are two important extensions to the numpy indexing functionality:

• Size 1 dimensions are never removed.

  An integer index i takes the i-th element but does not reduce the rank of the output array by one:

• When advanced indexing is used on more than one dimension, the advanced indices work independently.

  When more than one dimension’s slice is a 1-d boolean sequence or 1-d sequence of integers, then these indices work independently along each dimension (similar to the way vector subscripts work in Fortran), rather than by their elements:

Subspacing by coordinate values

Subspacing by values of 1-d coordinates allows a subspaced field to be defined via coordinate values of its domain.

Coordinate values are provided as keyword arguments to a call to the subspace attribute. Coordinates are identified by their identity or their dimension’s identifier in the field’s domain. Note that:

• The dimensions to be subspaced may be given in any order.
• Dimensions for which no subspacing is required need not be specified.
• Size 1 dimensions of the domain which are not spanned by the data array may be specified.

Examples

>>> print f
Data            : air_temperature(time(12), latitude(73), longitude(96)) K
Cell methods    : time: mean
Dimensions      : time(12) = [15, ..., 345] days since 1860-1-1
                : latitude(73) = [-90, ..., 90] degrees_north
                : longitude(96) = [0, ..., 356.25] degrees_east
                : height(1) = [2] m

>>> f.shape
(12, 73, 96)
>>> f.subspace[...].shape
(12, 73, 96)
>>> f.subspace[slice(0, 12), :, 10:0:-2].shape
(12, 73, 5)
>>> lon = f.coord('longitude').array
>>> f.subspace[..., lon<180]

>>> f.shape
(12, 73, 96)
>>> f.subspace[0, ...].shape
(1, 73, 96)
>>> f.subspace[3, slice(10, 0, -2), 95].shape
(1, 5, 1)

>>> f.shape
(12, 73, 96)
>>> f.subspace[:, [0, 72], [5, 4, 3]].shape
(12, 2, 3)

>>> f.subspace().shape
(12, 73, 96)
>>> f.subspace(latitude=0).shape
(12, 1, 96)
>>> f.subspace(latitude=cf.wi(-30, 30)).shape
(12, 25, 96)
>>> f.subspace(long=cf.ge(270, 'degrees_east'), lat=cf.set([0, 2.5, 10])).shape
(12, 3, 24)
>>> f.subspace(latitude=cf.lt(0, 'degrees_north'))
(12, 36, 96)
>>> f.subspace(latitude=[cf.lt(0, 'degrees_north'), 90])
(12, 37, 96)
>>> import math
>>> f.subspace(longitude=cf.lt(math.pi, 'radian'), height=2)
(12, 73, 48)
>>> f.subspace(height=cf.gt(3))
IndexError: No indices found for 'height' values gt 3

>>> f.subspace(dim2=3.75).shape
(12, 1, 96)