.. 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