nddata_arith¶

astroimtools.arithmetic.nddata_arith(nddata1, nddata2, operator, fill_value=0.0, keywords=None)[source]¶

Perform basic arithmetic on two NDData objects and return a new NDData object.

Parameters:

nddata1, nddata2NDData or scalar: The NDData objects (or scalar) on which to perform the arithmetic operation. Note that nddata1 and nddata2 cannot both be scalars.
operator{‘+’, ‘-’, ‘*’, ‘/’, ‘//’, ‘min’, ‘max’}: The operator to apply to the inputs.
fill_valuefloat, optional: The fill value used in the output data when the resultant value is masked. The default is 0.
keywordsstr or list of str, optional: List of keywords in the meta dictionaries of both input NDData objects to propagate the same as arithmetic.

Returns:

resultNDData: NDData object resulting from the arithmetic operation.

Examples

>>> from astroimtools import nddata_arith
>>> from astropy.nddata import NDData
>>> nd1 = NDData([0, 1, 2, 3, 4])
>>> nd2 = NDData([1, 7, 5, 4, 2])

>>> nd = nddata_arith(nd1, 5, '+')
>>> nd.data
array([5, 6, 7, 8, 9])

>>> nd = nddata_arith(nd1, 5, '*')
>>> nd.data
array([ 0,  5, 10, 15, 20])

>>> nd = nddata_arith(nd1, nd2, '+')
>>> nd.data
array([1, 8, 7, 7, 6])

>>> nd = nddata_arith(nd1, nd2, 'min')
>>> nd.data
array([0, 1, 2, 3, 2])

>>> nd = nddata_arith(nd1, 2, '/')
>>> nd.data  
array([0., 0.5, 1., 1.5, 2. ])

>>> nd = nddata_arith(nd1, 2, '//')
>>> nd.data
array([0, 0, 1, 1, 2])

The operand can also be applied to NDData meta keywords:

>>> nd1.meta['exptime'] = 500
>>> nd2.meta['exptime'] = 1000
>>> nd = nddata_arith(nd1, nd2, '+', keywords='exptime')
>>> nd.meta['exptime']
1500

And the NDData masks are used in the operations:

>>> nd1.mask = (nd1.data > 3)
>>> nd2.mask = (nd2.data < 2)
>>> nd = nddata_arith(nd1, nd2, '+')
>>> nd.data
array([0, 8, 7, 7, 0])
>>> nd.mask
array([ True, False, False, False,  True]...)

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nddata_arith¶