Return an ndarray of indices that sort the masked array along axis 0 in NumPy

To return an ndarray of indices that sort the array, use the ma.MaskedArray.argsort() method in Numpy. The axis is set using the "axis" parameter i.e. the Axis along which to sort.

Returns an Array of indices that sort a along the specified axis. In other words, a[index_array] yields a sorted a. The axis is the axis along which to sort. If None, the default, the flattened array is used. The order is when a is an array with fields defined, this argument specifies which fields to compare first, second, etc. Not all fields need be specified. The fill_value is the value used internally for the masked values. If fill_value is not None, it supersedes endwith.

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([[49, 85, 45], [67, 33, 59]])
print("Array...
", arr)
print("
Array type...
", arr.dtype)

Get the dimensions of the Array −

print("Array Dimensions...
",arr.ndim)

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

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

Return an ndarray of indices that sort the array, use the ma.MaskedArray.argsort() method in Numpy. The axis is set using the "axis" parameter i.e the Axis along which to sort. Here, axis is set with value 0 −

print("
Result...
",maskArr.argsort(axis = 0))

Example

import numpy as np
import numpy.ma as ma

# Create an array with int elements using the numpy.array() method
arr = np.array([[55, 85], [67, 33], [29, 88], [56, 45]])
print("Array...
", arr)
print("
Array type...
", arr.dtype)

# Get the dimensions of the Array
print("
Array Dimensions...
",arr.ndim)

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

# To return an ndarray of indices that sort the array, use the ma.MaskedArray.argsort() method in Numpy
# The axis is set using the "axis" parameter i.e the Axis along which to sort.
# Here, axis is set with value 0
print("
Result...
",maskArr.argsort(axis = 0))

Output

Array...
[[55 85]
[67 33]
[29 88]
[56 45]]

Array type...
int64

Array Dimensions...
2

Our Masked Array
[[-- 85]
[67 33]
[29 88]
[56 --]]

Our Masked Array type...
int64

Our Masked Array Dimensions...
2

Our Masked Array Shape...
(4, 2)

Elements in the Masked Array...
8

Result...
[[2 1]
[3 0]
[1 2]
[0 3]]