Bases: ndarray
A Quantity represents a number with some associated unit.
See also: https://docs.astropy.org/en/stable/units/quantity.html
ndarray, Quantity (sequence), or str
The numerical value of this quantity in the units given by unit. If a Quantity or sequence of them (or any other valid object with a unit attribute), creates a new Quantity object, converting to unit units as needed. If a string, it is converted to a number or Quantity, depending on whether a unit is present.
An object that represents the unit associated with the input value. Must be an UnitBase object or a string parseable by the units package.
dtype, optional
The dtype of the resulting Numpy array or scalar that will hold the value. If not provided, it is determined from the input, except that any integer and (non-Quantity) object inputs are converted to float by default. If None, the normal numpy.dtype introspection is used, e.g. preventing upcasting of integers.
If True (default), then the value is copied. Otherwise, a copy will only be made if __array__ returns a copy, if value is a nested sequence, or if a copy is needed to satisfy an explicitly given dtype. (The False option is intended mostly for internal use, to speed up initialization where a copy is known to have been made. Use with care.)
Specify the order of the array. As in array. This parameter is ignored if the input is a Quantity and copy=False.
If False (default), the returned array will be forced to be a Quantity. Otherwise, Quantity subclasses will be passed through, or a subclass appropriate for the unit will be used (such as Dex for u.dex(u.AA)).
int, optional
Specifies the minimum number of dimensions that the resulting array should have. Ones will be prepended to the shape as needed to meet this requirement. This parameter is ignored if the input is a Quantity and copy=False.
TypeError
If the value provided is not a Python numeric type.
TypeError
If the unit provided is not either a Unit object or a parseable string unit.
Notes
Quantities can also be created by multiplying a number or array with a Unit. See https://docs.astropy.org/en/latest/units/
Unless the dtype argument is explicitly specified, integer or (non-Quantity) object inputs are converted to float by default.
Attributes Summary
Methods Summary
Attributes Documentation
Returns a copy of the current Quantity instance with CGS units. The value of the resulting object will be scaled.
A list of equivalencies that will be applied by default during unit conversions.
A 1-D iterator over the Quantity array.
This returns a QuantityIterator instance, which behaves the same as the flatiter instance returned by flat, and is similar to, but not a subclass of, Python’s built-in iterator object.
Container for meta information like name, description, format. This is required when the object is used as a mixin column within a table, but can be used as a general way to store meta information.
True if the value of this quantity is a scalar, or False if it is an array-like object.
Note
This is subtly different from numpy.isscalar in that numpy.isscalar returns False for a zero-dimensional array (e.g. np.array(1)), while this is True for quantities, since quantities cannot represent true numpy scalars.
Returns a copy of the current Quantity instance with SI units. The value of the resulting object will be scaled.
A UnitBase object representing the unit of this quantity.
The numerical value of this instance.
See also
to_value
Get the numerical value in a given unit.
Methods Documentation
Returns True if all elements evaluate to True.
Refer to numpy.all for full documentation.
Returns True if any of the elements of a evaluate to True.
Refer to numpy.any for full documentation.
Return indices of the maximum values along the given axis.
Refer to numpy.argmax for full documentation.
Return indices of the minimum values along the given axis.
Refer to numpy.argmin for detailed documentation.
Returns the indices that would sort this array.
Refer to numpy.argsort for full documentation.
Use an index array to construct a new array from a set of choices.
Refer to numpy.choose for full documentation.
Generates a new Quantity with the units decomposed. Decomposed units have only irreducible units in them (see astropy.units.UnitBase.decompose).
UnitBase, optional
The bases to decompose into. When not provided, decomposes down to any irreducible units. When provided, the decomposed result will only contain the given units. This will raises a UnitsError if it’s not possible to do so.
Quantity
A new object equal to this quantity with units decomposed.
Not implemented, use .value.dump() instead.
Not implemented, use .value.dumps() instead.
Fill the array with a scalar value.
All elements of a will be assigned this value.
Examples
>>> import numpy as np >>> a = np.array([1, 2]) >>> a.fill(0) >>> a array([0, 0]) >>> a = np.empty(2) >>> a.fill(1) >>> a array([1., 1.])
Fill expects a scalar value and always behaves the same as assigning to a single array element. The following is a rare example where this distinction is important:
>>> a = np.array([None, None], dtype=object) >>> a[0] = np.array(3) >>> a array([array(3), None], dtype=object) >>> a.fill(np.array(3)) >>> a array([array(3), array(3)], dtype=object)
Where other forms of assignments will unpack the array being assigned:
>>> a[...] = np.array(3) >>> a array([3, 3], dtype=object)
Insert values along the given axis before the given indices and return a new Quantity object.
This is a thin wrapper around the numpy.insert function.
int, slice or sequence of int
Object that defines the index or indices before which values is inserted.
Values to insert. If the type of values is different from that of quantity, values is converted to the matching type. values should be shaped so that it can be broadcast appropriately The unit of values must be consistent with this quantity.
int, optional
Axis along which to insert values. If axis is None then the quantity array is flattened before insertion.
Quantity
A copy of quantity with values inserted. Note that the insertion does not occur in-place: a new quantity array is returned.
Examples
>>> import astropy.units as u >>> q = [1, 2] * u.m >>> q.insert(0, 50 * u.cm) <Quantity [ 0.5, 1., 2.] m>
>>> q = [[1, 2], [3, 4]] * u.m
>>> q.insert(1, [10, 20] * u.m, axis=0)
<Quantity [[ 1., 2.],
[ 10., 20.],
[ 3., 4.]] m>
>>> q.insert(1, 10 * u.m, axis=1)
<Quantity [[ 1., 10., 2.],
[ 3., 10., 4.]] m>
Copy an element of an array to a scalar Quantity and return it.
Like item() except that it always returns a Quantity, not a Python scalar.
Returns the average of the array elements along given axis.
Refer to numpy.mean for full documentation.
Set a.flat[n] = values[n] for all n in indices.
Refer to numpy.put for full documentation.
Return a with each element rounded to the given number of decimals.
Refer to numpy.around for full documentation.
Find indices where elements of v should be inserted in a to maintain order.
For full documentation, see numpy.searchsorted
Returns the standard deviation of the array elements along given axis.
Refer to numpy.std for full documentation.
Return an array formed from the elements of a at the given indices.
Refer to numpy.take for full documentation.
Return a new Quantity object with the specified unit.
An object that represents the unit to convert to. Must be an UnitBase object or a string parseable by the units package.
list of tuple
A list of equivalence pairs to try if the units are not directly convertible. See Equivalencies. If not provided or [], class default equivalencies will be used (none for Quantity, but may be set for subclasses) If None, no equivalencies will be applied at all, not even any set globally or within a context.
If True (default), then the value is copied. Otherwise, a copy will only be made if necessary.
See also
to_value
get the numerical value in a given unit.
Generate a string representation of the quantity and its unit.
The behavior of this function can be altered via the numpy.set_printoptions function and its various keywords. The exception to this is the threshold keyword, which is controlled via the [units.quantity] configuration item latex_array_threshold. This is treated separately because the numpy default of 1000 is too big for most browsers to handle.
Specifies the unit. If not provided, the unit used to initialize the quantity will be used.
The level of decimal precision. If None, or not provided, it will be determined from NumPy print options.
str, optional
The format of the result. If not provided, an unadorned string is returned. Supported values are:
‘latex’: Return a LaTeX-formatted string
‘latex_inline’: Return a LaTeX-formatted string that uses negative exponents instead of fractions
str, callable(), dict, optional
The formatter to use for the value. If a string, it should be a valid format specifier using Python’s mini-language. If a callable, it will be treated as the default formatter for all values and will overwrite default Latex formatting for exponential notation and complex numbers. If a dict, it should map a specific type to a callable to be directly passed into numpy.array2string. If not provided, the default formatter will be used.
str, optional
Subformat of the result. For the moment, only used for format='latex' and format='latex_inline'. Supported values are:
‘inline’: Use $ ... $ as delimiters.
‘display’: Use $\displaystyle ... $ as delimiters.
str
A string with the contents of this Quantity
The numerical value, possibly in a different unit.
The unit in which the value should be given. If not given or None, use the current unit.
list of tuple, optional
A list of equivalence pairs to try if the units are not directly convertible (see Equivalencies). If not provided or [], class default equivalencies will be used (none for Quantity, but may be set for subclasses). If None, no equivalencies will be applied at all, not even any set globally or within a context.
ndarray or scalar
The value in the units specified. For arrays, this will be a view of the data if no unit conversion was necessary.
See also
to
Get a new instance in a different unit.
Not implemented, use .value.tobytes() instead.
Not implemented, use .value.tofile() instead.
Return the array as an a.ndim-levels deep nested list of Python scalars.
Return a copy of the array data as a (nested) Python list. Data items are converted to the nearest compatible builtin Python type, via the item function.
If a.ndim is 0, then since the depth of the nested list is 0, it will not be a list at all, but a simple Python scalar.
object, or list of object, or list of list of object, or …
The possibly nested list of array elements.
Notes
The array may be recreated via a = np.array(a.tolist()), although this may sometimes lose precision.
Examples
For a 1D array, a.tolist() is almost the same as list(a), except that tolist changes numpy scalars to Python scalars:
>>> import numpy as np >>> a = np.uint32([1, 2]) >>> a_list = list(a) >>> a_list [np.uint32(1), np.uint32(2)] >>> type(a_list[0]) <class 'numpy.uint32'> >>> a_tolist = a.tolist() >>> a_tolist [1, 2] >>> type(a_tolist[0]) <class 'int'>
Additionally, for a 2D array, tolist applies recursively:
>>> a = np.array([[1, 2], [3, 4]]) >>> list(a) [array([1, 2]), array([3, 4])] >>> a.tolist() [[1, 2], [3, 4]]
The base case for this recursion is a 0D array:
>>> a = np.array(1) >>> list(a) Traceback (most recent call last): ... TypeError: iteration over a 0-d array >>> a.tolist() 1
Not implemented, use .value.tostring() instead.
Return the sum along diagonals of the array.
Refer to numpy.trace for full documentation.
Returns the variance of the array elements, along given axis.
Refer to numpy.var for full documentation.
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