.. currentmodule:: numpy.ma

.. _numpy.ma.constants:

Constants of the :mod:`numpy.ma` module
=======================================

In addition to the :class:`MaskedArray` class, the :mod:`numpy.ma` module
defines several constants.

.. data:: masked

   The :attr:`masked` constant is a special case of :class:`MaskedArray`,
   with a float datatype and a null shape. It is used to test whether a
   specific entry of a masked array is masked, or to mask one or several
   entries of a masked array::

   .. try_examples::

      >>> import numpy as np

      >>> x = np.ma.array([1, 2, 3], mask=[0, 1, 0])
      >>> x[1] is np.ma.masked
      True
      >>> x[-1] = np.ma.masked
      >>> x
      masked_array(data=[1, --, --],
                   mask=[False,  True,  True],
             fill_value=999999)


.. data:: nomask

   Value indicating that a masked array has no invalid entry.
   :attr:`nomask` is used internally to speed up computations when the mask
   is not needed. It is represented internally as ``np.False_``.


.. data:: masked_print_option

   String used in lieu of missing data when a masked array is printed.
   By default, this string is ``'--'``.

   Use ``set_display()`` to change the default string.
   Example usage: ``numpy.ma.masked_print_option.set_display('X')`` 
   replaces missing data with ``'X'``.

.. _maskedarray.baseclass:

The :class:`MaskedArray` class
==============================


.. class:: MaskedArray

A subclass of :class:`~numpy.ndarray` designed to manipulate numerical arrays with missing data.



An instance of :class:`MaskedArray` can be thought as the combination of several elements:

* The :attr:`~MaskedArray.data`, as a regular :class:`numpy.ndarray` of any shape or datatype (the data).
* A boolean :attr:`~numpy.ma.MaskedArray.mask` with the same shape as the data, where a ``True`` value indicates that the corresponding element of the data is invalid.
  The special value :const:`nomask` is also acceptable for arrays without named fields, and indicates that no data is invalid.
* A :attr:`~numpy.ma.MaskedArray.fill_value`, a value that may be used to replace the invalid entries in order to return a standard :class:`numpy.ndarray`.



.. _ma-attributes:

Attributes and properties of masked arrays
------------------------------------------

.. seealso:: :ref:`Array Attributes <arrays.ndarray.attributes>`

.. autoattribute:: numpy::ma.MaskedArray.data

.. autoattribute:: numpy::ma.MaskedArray.mask

.. autoattribute:: numpy::ma.MaskedArray.recordmask

.. autoattribute:: numpy::ma.MaskedArray.fill_value

.. autoattribute:: numpy::ma.MaskedArray.baseclass

.. autoattribute:: numpy::ma.MaskedArray.sharedmask

.. autoattribute:: numpy::ma.MaskedArray.hardmask

As :class:`MaskedArray` is a subclass of :class:`~numpy.ndarray`, a masked array also inherits all the attributes and properties of a  :class:`~numpy.ndarray` instance.

.. autosummary::
   :toctree: generated/

   MaskedArray.base
   MaskedArray.ctypes
   MaskedArray.dtype
   MaskedArray.flags

   MaskedArray.itemsize
   MaskedArray.nbytes
   MaskedArray.ndim
   MaskedArray.shape
   MaskedArray.size
   MaskedArray.strides

   MaskedArray.imag
   MaskedArray.real

   MaskedArray.flat
   MaskedArray.__array_priority__



:class:`MaskedArray` methods
============================

.. seealso:: :ref:`Array methods <array.ndarray.methods>`


Conversion
----------

.. autosummary::
   :toctree: generated/

   MaskedArray.__float__
   MaskedArray.__int__

   MaskedArray.view
   MaskedArray.astype
   MaskedArray.byteswap

   MaskedArray.compressed
   MaskedArray.filled
   MaskedArray.tofile
   MaskedArray.toflex
   MaskedArray.tolist
   MaskedArray.torecords
   MaskedArray.tobytes


Shape manipulation
------------------

For reshape, resize, and transpose, the single tuple argument may be
replaced with ``n`` integers which will be interpreted as an n-tuple.

.. autosummary::
   :toctree: generated/

   MaskedArray.flatten
   MaskedArray.ravel
   MaskedArray.reshape
   MaskedArray.resize
   MaskedArray.squeeze
   MaskedArray.swapaxes
   MaskedArray.transpose
   MaskedArray.T


Item selection and manipulation
-------------------------------

For array methods that take an ``axis`` keyword, it defaults to None.
If axis is None, then the array is treated as a 1-D array.
Any other value for ``axis`` represents the dimension along which
the operation should proceed.

.. autosummary::
   :toctree: generated/

   MaskedArray.argmax
   MaskedArray.argmin
   MaskedArray.argsort
   MaskedArray.choose
   MaskedArray.compress
   MaskedArray.diagonal
   MaskedArray.fill
   MaskedArray.item
   MaskedArray.nonzero
   MaskedArray.put
   MaskedArray.repeat
   MaskedArray.searchsorted
   MaskedArray.sort
   MaskedArray.take


Pickling and copy
-----------------

.. autosummary::
   :toctree: generated/

   MaskedArray.copy
   MaskedArray.dump
   MaskedArray.dumps


Calculations
------------

.. autosummary::
   :toctree: generated/

   MaskedArray.all
   MaskedArray.anom
   MaskedArray.any
   MaskedArray.clip
   MaskedArray.conj
   MaskedArray.conjugate
   MaskedArray.cumprod
   MaskedArray.cumsum
   MaskedArray.max
   MaskedArray.mean
   MaskedArray.min
   MaskedArray.prod
   MaskedArray.product
   MaskedArray.ptp
   MaskedArray.round
   MaskedArray.std
   MaskedArray.sum
   MaskedArray.trace
   MaskedArray.var


Arithmetic and comparison operations
------------------------------------

.. index:: comparison, arithmetic, operation, operator

Comparison operators:
~~~~~~~~~~~~~~~~~~~~~

.. autosummary::
   :toctree: generated/

   MaskedArray.__lt__
   MaskedArray.__le__
   MaskedArray.__gt__
   MaskedArray.__ge__
   MaskedArray.__eq__
   MaskedArray.__ne__

Truth value of an array (:class:`bool() <bool>`):
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

.. autosummary::
   :toctree: generated/

   MaskedArray.__bool__


Arithmetic:
~~~~~~~~~~~

.. autosummary::
   :toctree: generated/

   MaskedArray.__abs__
   MaskedArray.__add__
   MaskedArray.__radd__
   MaskedArray.__sub__
   MaskedArray.__rsub__
   MaskedArray.__mul__
   MaskedArray.__rmul__
   MaskedArray.__truediv__
   MaskedArray.__rtruediv__
   MaskedArray.__floordiv__
   MaskedArray.__rfloordiv__
   MaskedArray.__mod__
   MaskedArray.__rmod__
   MaskedArray.__divmod__
   MaskedArray.__rdivmod__
   MaskedArray.__pow__
   MaskedArray.__rpow__
   MaskedArray.__lshift__
   MaskedArray.__rlshift__
   MaskedArray.__rshift__
   MaskedArray.__rrshift__
   MaskedArray.__and__
   MaskedArray.__rand__
   MaskedArray.__or__
   MaskedArray.__ror__
   MaskedArray.__xor__
   MaskedArray.__rxor__


Arithmetic, in-place:
~~~~~~~~~~~~~~~~~~~~~

.. autosummary::
   :toctree: generated/

   MaskedArray.__iadd__
   MaskedArray.__isub__
   MaskedArray.__imul__
   MaskedArray.__itruediv__
   MaskedArray.__ifloordiv__
   MaskedArray.__imod__
   MaskedArray.__ipow__
   MaskedArray.__ilshift__
   MaskedArray.__irshift__
   MaskedArray.__iand__
   MaskedArray.__ior__
   MaskedArray.__ixor__


Representation
--------------

.. autosummary::
   :toctree: generated/

   MaskedArray.__repr__
   MaskedArray.__str__

   MaskedArray.ids
   MaskedArray.iscontiguous


Special methods
---------------

For standard library functions:

.. autosummary::
   :toctree: generated/

   MaskedArray.__copy__
   MaskedArray.__deepcopy__
   MaskedArray.__getstate__
   MaskedArray.__reduce__
   MaskedArray.__setstate__

Basic customization:

.. autosummary::
   :toctree: generated/

   MaskedArray.__new__
   MaskedArray.__array__
   MaskedArray.__array_wrap__

Container customization: (see :ref:`Indexing <arrays.indexing>`)

.. autosummary::
   :toctree: generated/

   MaskedArray.__len__
   MaskedArray.__getitem__
   MaskedArray.__setitem__
   MaskedArray.__delitem__
   MaskedArray.__contains__



Specific methods
----------------

Handling the mask
~~~~~~~~~~~~~~~~~

The following methods can be used to access information about the mask or to
manipulate the mask.

.. autosummary::
   :toctree: generated/

   MaskedArray.__setmask__

   MaskedArray.harden_mask
   MaskedArray.soften_mask
   MaskedArray.unshare_mask
   MaskedArray.shrink_mask


Handling the `fill_value`
~~~~~~~~~~~~~~~~~~~~~~~~~

.. autosummary::
   :toctree: generated/

   MaskedArray.get_fill_value
   MaskedArray.set_fill_value



Counting the missing elements
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

.. autosummary::
   :toctree: generated/

   MaskedArray.count
