Compute the median of the masked array elements along specified axis in Numpy

To compute the median of the masked array elements along specific axis, use the MaskedArray.median() method in Python Numpy −

• The axis is set using the "axis" parameter
• The axis is axis along which the medians are computed.
• The default (None) is to compute the median along a flattened version of the array.

The overwrite_input parameter, if True, then allow use of memory of input array (a) for calculations. The input array will be modified by the call to median. This will save memory when you do not need to preserve the contents of the input array. Treat the input as undefined, but it will probably be fully or partially sorted. Default is False. Note that, if overwrite_input is True, and the input is not already an ndarray, an error will be raised.

Steps

At first, import the required library −

import numpy as np
import numpy.ma as ma

Create an array with int elements using the numpy.array() method −

arr = np.array([[65, 68, 81], [93, 33, 76], [73, 88, 51], [62, 45, 67]])
print("Array...
", arr)

Create a masked array and mask some of them as invalid −

maskArr = ma.masked_array(arr, mask =[[1, 1, 0], [ 0, 0, 0], [0, 1, 0], [0, 1, 0]])
print("
Our Masked Array...
", maskArr)

Get the type of the masked array −

print("
Our Masked Array type...
", maskArr.dtype)

Get the dimensions of the Masked Array −

print("
Our Masked Array Dimensions...
",maskArr.ndim)

Get the shape of the Masked Array −

print("
Our Masked Array Shape...
",maskArr.shape)

Get the number of elements of the Masked Array −

print("
Number of elements in the Masked Array...
",maskArr.size)

To compute the median of the masked array elements along specific axis, use the MaskedArray.median() method. The axis is set using the "axis" parameter. The axis is axis along which the medians are computed. The default (None) is to compute the median along a flattened version of the array −

resArr = np.ma.median(maskArr, axis = 1)
print("
Resultant Array..
.", resArr)

Example

import numpy as np
import numpy.ma as ma

# Create an array with int elements using the numpy.array() method
arr = np.array([[65, 68, 81], [93, 33, 76], [73, 88, 51], [62, 45, 67]])
print("Array...
", arr)

# Create a masked array and mask some of them as invalid
maskArr = ma.masked_array(arr, mask =[[1, 1, 0], [ 0, 0, 0], [0, 1, 0], [0, 1, 0]])
print("
Our Masked Array...
", maskArr)

# Get the type of the masked array
print("
Our Masked Array type...
", maskArr.dtype)

# Get the dimensions of the Masked Array
print("
Our Masked Array Dimensions...
",maskArr.ndim)

# Get the shape of the Masked Array
print("
Our Masked Array Shape...
",maskArr.shape)

# Get the number of elements of the Masked Array
print("
Number of elements in the Masked Array...
",maskArr.size)

# To compute the median of the masked array elements along specific axis, use the MaskedArray.median() method in Python Numpy
# The axis is set using the "axis" parameter
# The axis is axis along which the medians are computed.
# The default (None) is to compute the median along a flattened version of the array.
resArr = np.ma.median(maskArr, axis = 1)
print("
Resultant Array..
.", resArr)

Output

Array...
[[65 68 81]
[93 33 76]
[73 88 51]
[62 45 67]]

Our Masked Array...
[[-- -- 81]
[93 33 76]
[73 -- 51]
[62 -- 67]]

Our Masked Array type...
int64

Our Masked Array Dimensions...
2

Our Masked Array Shape...
(4, 3)

Number of elements in the Masked Array...
12

Resultant Array..
. [81.0 76.0 62.0 64.5]