30 Mar Sorting Numpy Arrays

Posted at 22:51h in Numpy by

The numpy.sort() function is used in Numpy to sort arrays in a sequence. This sequence can be ascending or descending. Here, we will see how to,

  1. Sort (Ascending order) a 1D integer array in NumPy
  2. Sort (Descending order) a 1D integer array in NumPy
  3. Sort (Ascending order) a 1D string array in NumPy
  4. Sort (Ascending order) a 1D string array in NumPy
  5. Sort a 2D array in NumPy (axis = 1)
  6. Sort a 2D array in NumPy (axis = 0)
  7. Sort a 3D array in NumPy(axis = 1)
  8. Sort a 3D array in NumPy(axis = 0)
  9. Sort a 3D array in NumPy(axis = 2)

Let us start with the examples:

Sort (Ascending order) a 1D integer array in NumPy

# Sort a 1d integer array in NumPy
# Ascending order sort (default)

import numpy as np

n = np.array([75, 89, 32, 54, 12, 8, 45, 78])

# sort
print("Sorted array = ",np.sort(n))

Output

Sorted array =  [ 8 12 32 45 54 75 78 89]

Sort (Descending order) a 1D integer array in NumPy

# Sort a 1d integer array in NumPy
# Descending order sort

import numpy as np

n = np.array([75, 89, 32, 54, 12, 8, 45, 78])

# sort
print("Sorted array = ",np.sort(n)[::-1])

Output

Sorted array =  [89 78 75 54 45 32 12  8]

Sort (Ascending order) a 1D string array in NumPy

# Sort a 1d string array in NumPy
# Ascending order sort (default)

import numpy as np

n = np.array(["John", "Amit", "Virat", "Rohit", "Dhoni"])

# sort
print("Sorted array = ",np.sort(n))

Output

Sorted array =  ['Amit' 'Dhoni' 'John' 'Rohit' 'Virat']

Sort (Descending order) a 1D string array in NumPy

# Sort a 1d string array in NumPy
# Descending order sort

import numpy as np

n = np.array(["John", "Amit", "Virat", "Rohit", "Dhoni"])

# sort
print("Sorted array = ",np.sort(n)[::-1])

Output

Sorted array =  ['Virat' 'Rohit' 'John' 'Dhoni' 'Amit']

Sort a 2D array in NumPy (axis = 1)

# Sort a 2d array in NumPy
# Sorts elements horizontally (axis = 1) along each row

import numpy as np

# Create a 2d array
n = np.array([[20, 10, 98, 7],
              [42, 18, 2, 78],
              [5, 38, 142, 88]
              ])

# sort
print("Sorted array =\n",np.sort(n, axis = 1))

Output

Sorted array =
 [[  7  10  20  98]
 [  2  18  42  78]
 [  5  38  88 142]]

Sort a 2D array in NumPy (axis = 0)

# Sort a 2d array in NumPy
# Sorts elements vertically (axis = 0) along each row

import numpy as np

# Create a 2d array
n = np.array([[20, 10, 98, 7],
              [42, 18, 2, 78],
              [5, 38, 142, 88]
              ])

# sort
print("Sorted array =\n",np.sort(n, axis = 0))

Output

Sorted array =
 [[  5  10   2   7]
 [ 20  18  98  78]
 [ 42  38 142  88]]

Sort a 3D array in NumPy(axis = 1)

# Sort a 3d array in NumPy
# axis = 1 sorts elements vertically withing each individual matrix
# individual matrix

import numpy as np

n = np.array([[
               [130, 40, 99],
               [4, 55, 70]],
              [
               [1020, 890, 990],
               [100, 10, 120]]
             ])

# sort
print("Sorted array = ",np.sort(n, axis = 1))

Output

Sorted array =
 [[[   4   40   70]
  [ 130   55   99]]

 [[ 100   10  120]
  [1020  890  990]]]

Sort a 3D array in NumPy(axis = 0)

# Sort a 3d array in NumPy
# axis = 0 sorts elements in the same (row,col) position across all matrices in the stack
# across all matrices

import numpy as np

n = np.array([[
               [130, 40, 99],
               [4, 55, 70]],
              [
               [1020, 890, 990],
               [100, 10, 120]]
             ])

# sort
print("Sorted array =\n",np.sort(n, axis = 0))

Output

Sorted array =
 [[[ 130   40   99]
  [   4   10   70]]

 [[1020  890  990]
  [ 100   55  120]]]

Sort a 3D array in NumPy(axis = 2)

# Sort a 3d array in NumPy
# axis = 2 (default) sorts elements horizontally within each individual matrix
# individual matrix

import numpy as np

n = np.array([[
               [130, 40, 99],
               [4, 55, 70]],
              [
               [1020, 890, 990],
               [100, 10, 120]]
             ])

# sort
print("Sorted array =\n",np.sort(n, axis = 2))

Output

Sorted array =
 [[[  40   99  130]
  [   4   55   70]]

 [[ 890  990 1020]
  [  10  100  120]]]

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Search a Numpy Array for a value
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