Insert Row/Columns, Append Row/Columns, Array Manipulation

np.insert() — insert elements/rows/columns

import numpy as np

a = np.array([10, 20, 30, 40])
b = np.insert(a, 2, 99)          # insert 99 at index 2
print(b)                           # [10 20 99 30 40]

m = np.array([[1, 2], [3, 4]])
row_inserted = np.insert(m, 1, [9, 9], axis=0)     # insert a new row at index 1
print(row_inserted)
# [[1 2]
#  [9 9]
#  [3 4]]

col_inserted = np.insert(m, 1, [8, 8], axis=1)     # insert a new column at index 1
print(col_inserted)
# [[1 8 2]
#  [3 8 4]]

np.append() — append elements/rows/columns to the end

a = np.array([1, 2, 3])
b = np.append(a, [4, 5])
print(b)   # [1 2 3 4 5]

m = np.array([[1, 2], [3, 4]])
new_row = np.append(m, [[5, 6]], axis=0)
print(new_row)
# [[1 2]
#  [3 4]
#  [5 6]]

new_col = np.append(m, [[7], [8]], axis=1)
print(new_col)
# [[1 2 7]
#  [3 4 8]]

np.delete() — remove elements/rows/columns

a = np.array([10, 20, 30, 40])
print(np.delete(a, 1))          # [10 30 40]  -- removes index 1

m = np.array([[1, 2], [3, 4], [5, 6]])
print(np.delete(m, 1, axis=0))    # removes row index 1
print(np.delete(m, 0, axis=1))    # removes column index 0

Array Manipulation Operations

a = np.array([[1, 2], [3, 4]])

print(a.T)                    # transpose -- swap rows and columns
# [[1 3]
#  [2 4]]

b = np.array([1, 2, 3])
c = np.array([4, 5, 6])
print(np.concatenate([b, c]))   # [1 2 3 4 5 6]

print(np.vstack([b, c]))          # stack vertically -> 2 rows
# [[1 2 3]
#  [4 5 6]]

print(np.hstack([b, c]))            # stack horizontally -> [1 2 3 4 5 6]

print(np.split(np.arange(9), 3))      # split into 3 equal parts
# [array([0,1,2]), array([3,4,5]), array([6,7,8])]

print(np.sort(np.array([5, 2, 8, 1])))  # [1 2 5 8]

print(np.unique(np.array([1, 2, 2, 3, 3, 3])))   # [1 2 3]

Quick reference table