In the first part of Operations on Numpy Arrays, you learned about slicing, indexing, and arithmetic operations. This chapter will introduce you to some very important operations on NumPy arrays that are requently used in Data Science.

Statistical Operations on NumPy arrays

NumPy contains various in-built functions to get statistical information regarding the array such as max value, min value, mean, median, etc. Below is a list of such functions:

import numpy as np

# Creating a 1-D NumPy array
arr1 = np.arange(start=1, stop=5, step=1)

# Printing the array
print("arr1: ", arr1)

# Min value
print("Min: ", np.min(arr1))

# Max Value
print("Max: ", np.max(arr1))

# Mean
print("Mean: ", np.mean(arr1))

# Median
print("Median: ", np.median(arr1))

# Standard Deviation
print("Standard Deviation: ", np.std(arr1))

# Get unique values and their counts
uniqs, counts = np.unique(arr1, return_counts=True)
print("Unique values: ", uniqs)
print("Count of respective unique values: ", counts)

arr1: [1 2 3 4]
Min: 1
Max: 4
Mean: 2.5
Median: 2.5
Standard Deviation: 1.118033988749895
Unique values: [1 2 3 4]
Count of respective unique values: [1 1 1 1]

Transformation Operations on NumPy arrays

Various operations can be performed to transform the shape and order of elements in a NumPy array.

import numpy as np

# Creating a 1-D numpy array
arr = np.array([6, 5, 4, 3, 2, 1])

# Print the array
print("arr:\n", arr)
print("Shape of arr: ", arr.shape)
print("\n")

# Sort the array in ascending order
print("Sorted array: ", np.sort(arr))
print("\n")

# Change the array shape to (2, 3)
reshaped_arr = arr.reshape(2, 3)
print("Reshaped array: ", reshaped_arr)
print("Shape of reshaped array: ", reshaped_arr.shape)
print("\n")

# Transform the reshaped array
transposed_arr = reshaped_arr.transpose()
print("Transopose array: ", transposed_arr)
print("Shape of transposed array: ", transposed_arr.shape)
print("\n")

# Change the reshaped array (which is 2-D) to 1-D
flattened_arr = reshaped_arr.flatten()
print("Flattened array: ", flattened_arr)

arr:
[6 5 4 3 2 1]
Shape of arr: (6,)

Sorted array: [1 2 3 4 5 6]

Reshaped array: [[6 5 4]
[3 2 1]]
Shape of reshaped array: (2, 3)

Transopose array: [[6 3]
[5 2]
[4 1]]
Shape of transposed array: (3, 2)

Flattened array: [6 5 4 3 2 1]

This is it for operations on NumPy arrays. Head on to the next chapter to learn about ‘Input/Output operations in NumPy‘.