In addition to the
class, the
module defines several constants.
numpy.ma.masked
The
constant is a special case of
, 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::>>> importnumpyasnp>>> x=np.ma.array([1,2,3],mask=[0,1,0])>>> x[1]isnp.ma.maskedTrue>>> x[-1]=np.ma.masked>>> xmasked_array(data=[1, --, --], mask=[False, True, True], fill_value=999999)numpy.ma.nomask
Value indicating that a masked array has no invalid entry.
is used internally to speed up computations when the mask is not needed. It is represented internally as np.False_.
numpy.ma.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'.
The
class
classnumpy.ma.MaskedArray
A subclass of
designed to manipulate numerical arrays with missing data.
An instance of
can be thought as the combination of several elements:
The
, as a regular
of any shape or datatype (the data).
A boolean
with the same shape as the data, where a True value indicates that the corresponding element of the data is invalid. The special value
is also acceptable for arrays without named fields, and indicates that no data is invalid.
A
, a value that may be used to replace the invalid entries in order to return a standard
.
Attributes and properties of masked arrays
ma.MaskedArray.data
Returns the underlying data, as a view of the masked array.
If the underlying data is a subclass of
, it is returned as such.
>>> x=np.ma.array(np.matrix([[1,2],[3,4]]),mask=[[0,1],[1,0]])>>> x.datamatrix([[1, 2], [3, 4]])The type of the data can be accessed through the
attribute.
ma.MaskedArray.mask
Current mask.
ma.MaskedArray.recordmask
Get or set the mask of the array if it has no named fields. For structured arrays, returns an ndarray of booleans where entries are True if all the fields are masked, False otherwise:
>>> x=np.ma.array([(1,1),(2,2),(3,3),(4,4),(5,5)],... mask=[(0,0),(1,0),(1,1),(0,1),(0,0)],... dtype=[('a',int),('b',int)])>>> x.recordmaskarray([False, False, True, False, False])ma.MaskedArray.fill_value
The filling value of the masked array is a scalar. When setting, None will set to a default based on the data type.
Examples
>>> importnumpyasnp>>> fordtin[np.int32,np.int64,np.float64,np.complex128]:... np.ma.array([0,1],dtype=dt).get_fill_value()...np.int64(999999)np.int64(999999)np.float64(1e+20)np.complex128(1e+20+0j)>>> x=np.ma.array([0,1.],fill_value=-np.inf)>>> x.fill_valuenp.float64(-inf)>>> x.fill_value=np.pi>>> x.fill_valuenp.float64(3.1415926535897931)Reset to default:
>>> x.fill_value=None>>> x.fill_valuenp.float64(1e+20)ma.MaskedArray.baseclass
Class of the underlying data (read-only).
ma.MaskedArray.sharedmask
Share status of the mask (read-only).
ma.MaskedArray.hardmask
Specifies whether values can be unmasked through assignments.
By default, assigning definite values to masked array entries will unmask them. When
is True, the mask will not change through assignments.
Examples
>>> importnumpyasnp>>> x=np.arange(10)>>> m=np.ma.masked_array(x,x>5)>>> assertnotm.hardmaskSince m has a soft mask, assigning an element value unmasks that element:
>>> m[8]=42>>> mmasked_array(data=[0, 1, 2, 3, 4, 5, --, --, 42, --], mask=[False, False, False, False, False, False, True, True, False, True], fill_value=999999)After hardening, the mask is not affected by assignments:
>>> hardened=np.ma.harden_mask(m)>>> assertm.hardmaskandhardenedism>>> m[:]=23>>> mmasked_array(data=[23, 23, 23, 23, 23, 23, --, --, 23, --], mask=[False, False, False, False, False, False, True, True, False, True], fill_value=999999)As
is a subclass of
, a masked array also inherits all the attributes and properties of a
instance.
Base object if memory is from some other object.
An object to simplify the interaction of the array with the ctypes module.
Data-type of the array's elements.
Information about the memory layout of the array.
Length of one array element in bytes.
Total bytes consumed by the elements of the array.
Number of array dimensions.
Tuple of array dimensions.
Number of elements in the array.
Tuple of bytes to step in each dimension when traversing an array.
The imaginary part of the masked array.
The real part of the masked array.
Return a flat iterator, or set a flattened version of self to value.
MaskedArray.__array_priority__
methods
Conversion
()
Convert to float.
()
Convert to int.
([dtype, type, fill_value])
Return a view of the MaskedArray data.
(dtype[, order, casting, ...])
Copy of the array, cast to a specified type.
([inplace])
Swap the bytes of the array elements
()
Return all the non-masked data as a 1-D array.
([fill_value])
Return a copy of self, with masked values filled with a given value.
(fid[, sep, format])
Save a masked array to a file in binary format.
()
Transforms a masked array into a flexible-type array.
([fill_value])
Return the data portion of the masked array as a hierarchical Python list.
()
Transforms a masked array into a flexible-type array.
([fill_value, order])
Return the array data as a string containing the raw bytes in the array.
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.
([order])
Return a copy of the array collapsed into one dimension.
([order])
Returns a 1D version of self, as a view.
(*s, **kwargs)
Returns a reshaped masked array without changing its data.
(newshape[, refcheck, order])
([axis])
Remove axes of length one from a.
(axis1, axis2, /)
Return a view of the array with axis1 and axis2 interchanged.
(*axes)
Returns a view of the array with axes transposed.
View of the transposed array.
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.
([axis, fill_value, out, ...])
Returns array of indices of the maximum values along the given axis.
([axis, fill_value, out, ...])
Return array of indices to the minimum values along the given axis.
([axis, kind, order, ...])
Return an ndarray of indices that sort the array along the specified axis.
(choices[, out, mode])
Use an index array to construct a new array from a set of choices.
(condition[, axis, out])
Return a where condition is True.
([offset, axis1, axis2])
Return specified diagonals.
(value)
Fill the array with a scalar value.
(*args)
Copy an element of an array to a standard Python scalar and return it.
()
Return the indices of unmasked elements that are not zero.
(indices, values[, mode])
Set storage-indexed locations to corresponding values.
(repeats[, axis])
Repeat elements of an array.
(v[, side, sorter])
Find indices where elements of v should be inserted in a to maintain order.
([axis, kind, order, ...])
Sort the array, in-place
(indices[, axis, out, mode])
Take elements from a masked array along an axis.
Pickling and copy
Calculations
([axis, out, keepdims])
Returns True if all elements evaluate to True.
([axis, dtype])
Compute the anomalies (deviations from the arithmetic mean) along the given axis.
([axis, out, keepdims])
Returns True if any of the elements of a evaluate to True.
([min, max, out])
Return an array whose values are limited to [min,max].
()
Complex-conjugate all elements.
()
Return the complex conjugate, element-wise.
([axis, dtype, out])
Return the cumulative product of the array elements over the given axis.
([axis, dtype, out])
Return the cumulative sum of the array elements over the given axis.
([axis, out, fill_value, ...])
Return the maximum along a given axis.
([axis, dtype, out, keepdims])
Returns the average of the array elements along given axis.
([axis, out, fill_value, ...])
Return the minimum along a given axis.
([axis, dtype, out, keepdims])
Return the product of the array elements over the given axis.
([axis, dtype, out, keepdims])
Return the product of the array elements over the given axis.
([axis, out, fill_value, ...])
Return (maximum - minimum) along the given dimension (i.e. peak-to-peak value).
([decimals, out])
Return each element rounded to the given number of decimals.
([axis, dtype, out, ddof, ...])
Returns the standard deviation of the array elements along given axis.
([axis, dtype, out, keepdims])
Return the sum of the array elements over the given axis.
([offset, axis1, axis2, ...])
Return the sum along diagonals of the array.
([axis, dtype, out, ddof, ...])
Compute the variance along the specified axis.
Arithmetic and comparison operations
Comparison operators:
(other)
Return self<value.
(other)
Return self<=value.
(other)
Return self>value.
(other)
Return self>=value.
(other)
Check whether other equals self elementwise.
(other)
Check whether other does not equal self elementwise.
Truth value of an array (
):
Arithmetic:
(self)
(other)
Add self to other, and return a new masked array.
(other)
Add other to self, and return a new masked array.
(other)
Subtract other from self, and return a new masked array.
(other)
Subtract self from other, and return a new masked array.
(other)
Multiply self by other, and return a new masked array.
(other)
Multiply other by self, and return a new masked array.
(other)
Divide other into self, and return a new masked array.
(other)
Divide self into other, and return a new masked array.
(other)
Divide other into self, and return a new masked array.
(other)
Divide self into other, and return a new masked array.
(value, /)
Return self%value.
(value, /)
Return value%self.
(value, /)
Return divmod(self, value).
(value, /)
Return divmod(value, self).
(other)
Raise self to the power other, masking the potential NaNs/Infs
(other)
Raise other to the power self, masking the potential NaNs/Infs
(value, /)
Return self<<value.
(value, /)
Return value<<self.
(value, /)
Return self>>value.
(value, /)
Return value>>self.
(value, /)
Return self&value.
(value, /)
Return value&self.
(value, /)
Return self|value.
(value, /)
Return value|self.
(value, /)
Return self^value.
(value, /)
Return value^self.
Arithmetic, in-place:
(other)
Add other to self in-place.
(other)
Subtract other from self in-place.
(other)
Multiply self by other in-place.
(other)
True divide self by other in-place.
(other)
Floor divide self by other in-place.
(value, /)
Return self%=value.
(other)
Raise self to the power other, in place.
(value, /)
Return self<<=value.
(value, /)
Return self>>=value.
(value, /)
Return self&=value.
(value, /)
Return self|=value.
(value, /)
Return self^=value.
Representation
Special methods
For standard library functions:
Basic customization:
Container customization: (see
)
Specific methods
Handling the mask
The following methods can be used to access information about the mask or to manipulate the mask.
Handling the fill_value
Counting the missing elements