Importing NumPy

import numpy as np

Creating Arrays

# Create a 1-D array
arr = np.array([1, 2, 3])

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

# Create an array with zeros
arr = np.zeros((3, 4))

# Create an array with ones
arr = np.ones((2, 3))

# Create an array with random values
arr = np.random.random((2, 3))

Accessing Array Elements

# Access an element of a 1-D array
arr = np.array([1, 2, 3])
print(arr[0]) # 1

# Access a slice of a 1-D array
arr = np.array([1, 2, 3, 4, 5])
print(arr[1:4]) # [2, 3, 4]

# Access an element of a 2-D array
arr = np.array([[1, 2, 3], [4, 5, 6]])
print(arr[0, 1]) # 2

# Access a slice of a 2-D array
arr = np.array([[1, 2, 3], [4, 5, 6], [7, 8, 9]])
print(arr[0:2, 1:3]) # [[2, 3], [5, 6]]

Reshaping Arrays

arr = np.array([1, 2, 3, 4, 5, 6])
new_arr = arr.reshape(2, 3)

Flattening Arrays

arr = np.array([[1, 2], [3, 4], [5, 6]])
new_arr = arr.ravel()

Transposing Arrays

arr = np.array([[1, 2], [3, 4]])
new_arr = arr.transpose()

Basic Array Operations

arr1 = np.array([1, 2, 3])
arr2 = np.array([4, 5, 6])
new_arr = arr1 + arr2

Mathematical Functions

arr = np.array([1, 2, 3])
new_arr = np.sqrt(arr)

Statistical Functions

arr = np.array([1, 2, 3, 4, 5, 6])
mean = np.mean(arr)

Linear Algebra

arr1 = np.array([[1, 2], [3, 4]])
arr2 = np.array([[5, 6], [7, 8]])
new_arr = np.dot(arr1, arr2)

Saving and Loading Arrays

arr = np.array([1, 2, 3, 4, 5])
np.save('my_array', arr)
arr = np.load('my_array.npy')

Broadcasting

arr1 = np.array([1, 2, 3])
arr2 = 2
new_arr = arr1 * arr2

Concatenating Arrays

arr1 = np.array([[1, 2], [3, 4]])
arr2 = np.array([[5, 6], [7, 8]])
new_arr = np.concatenate((arr1, arr2))

Stacking Arrays

arr1 = np.array([[1, 2], [3, 4]])
arr2 = np.array([[5, 6], [7, 8]])
new_arr = np.hstack((arr1, arr2))

Slicing and Masking

arr = np.array([1, 2, 3, 4, 5])
new_arr = arr[arr > 2]

Unique Values

arr = np.array([1, 2, 1, 3, 4, 2, 5, 6, 5])
new_arr = np.unique(arr)

Sorting Arrays

arr = np.array([3, 2, 1, 4, 6, 5])
new_arr = np.sort(arr)

File Input and Output

arr = np.array([1, 2, 3, 4, 5])
np.savetxt('my_array.txt', arr)
arr = np.loadtxt('my_array.txt')

Fourier Transforms

import matplotlib.pyplot as plt

t = np.linspace(0, 1, 100)
y = np.sin(2 * np.pi * 5 * t)
fft_y = np.fft.fft(y)

plt.plot(fft_y)

Masked Arrays

arr = np.array([1, 2, -999, 4, -999, 6])
mask = arr != -999
new_arr = arr[mask]

Reference

Numpy Official Documentation