How to use NumPy Joining Array?

Question

ICSM Computer · Answer

Easy guide to joining arrays in NumPy (combining two or more arrays into one).
NumPy provides multiple ways to join arrays depending on the shape and how you want to merge them.
1. Using np.concatenate()
This is the most common way to join arrays.
Example — Join 1D Arrays
import numpy as np
a = np.array([1, 2, 3])
b = np.array([4, 5, 6])
result = np.concatenate((a, b))
print(result)
Output:
[1 2 3 4 5 6]
Example — Join 2D Arrays (Row-wise)
a = np.array([[1, 2], [3, 4]])
b = np.array([[5, 6], [7, 8]])
result = np.concatenate((a, b), axis=0)
print(result)
Output:
[[1 2]
 [3 4]
 [5 6]
 [7 8]]
Example — Join 2D Arrays (Column-wise)
result = np.concatenate((a, b), axis=1)
print(result)
Output:
[[1 2 5 6]
 [3 4 7 8]]
2. Using np.stack()
Creates a new dimension.
Example:
a = np.array([1, 2, 3])
b = np.array([4, 5, 6])
result = np.stack((a, b), axis=0)
print(result)
Output:
[[1 2 3]
 [4 5 6]]
Here, arrays are stacked into 2 rows.
3. Using np.hstack() (Horizontal Stack)
Joins arrays side by side.
a = np.array([1, 2, 3])
b = np.array([4, 5, 6])
result = np.hstack((a, b))
print(result)
Output:
[1 2 3 4 5 6]
For 2D arrays, it stacks column-wise.
4. Using np.vstack() (Vertical Stack)
Joins arrays top to bottom.
a = np.array([1, 2, 3])
b = np.array([4, 5, 6])
result = np.vstack((a, b))
print(result)
Output:
[[1 2 3]
 [4 5 6]]
5. Using np.dstack() (Depth Stack)
Stacks arrays into depth (3rd dimension).
a = np.array([1, 2, 3])
b = np.array([4, 5, 6])
result = np.dstack((a, b))
print(result)
Output:
[[[1 4]
  [2 5]
  [3 6]]]
Summary Table
Function
Behavior
concatenate()
Join along existing axis
stack()
Join but create a new axis
hstack()
Join horizontally
vstack()
Join vertically
dstack()
Join depth-wise (3D)

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How to use NumPy Joining Array?

ICSM Computer

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1 Answers

1. Using `np.concatenate()`

Example — Join 1D Arrays

Example — Join 2D Arrays (Row-wise)

Example — Join 2D Arrays (Column-wise)

2. Using `np.stack()`

Example:

3. Using `np.hstack()` (Horizontal Stack)

4. Using `np.vstack()` (Vertical Stack)

5. Using `np.dstack()` (Depth Stack)

Summary Table

Liked By

Function	Behavior
`concatenate()`	Join along existing axis
`stack()`	Join but create a new axis
`hstack()`	Join horizontally
`vstack()`	Join vertically
`dstack()`	Join depth-wise (3D)