How to use NumPy Array Slicing?

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Anubhav Sharma · Answer

What is Slicing? Slicing lets you extract a portion of an array — like substring slicing in Python. Syntax: start → index to begin (inclusive)end → index to stop (exclusive)step → how many to skip 1. Slicing a 1-D Array Example: a) Basic slicing Output: b) Without start Output: c) Without end Output: d) With step Output: e) Reverse slicing Output: 2. Slicing a 2-D Array a) Slice specific row Output: b) Slice specific column Output: c) Slice a sub-matrix Output: This extracts rows 0–1 and columns 1–2. 3. Slicing With Steps (2D) Example: Every 2nd row and column Output: 4. Slicing Higher-Dimensional Arrays (3D) If you have a 3D array (like an image): Get 1st "layer": Get middle column of every layer: Summary Cheatsheet Operation Example Meaning a[start:end] a[1:4] From 1 to 3 a[:end] a[:3] From 0 to 2 a[start:] a[2:] From 2 to end a[::step] a[::2] Every 2nd element a[::-1] Reverse array a[row, col] a[1,2] Element at row 1 col 2 a[rows, cols] a[0:2, 1:3] Sub-matrix

Operation	Example	Meaning
`a[start:end]`	`a[1:4]`	From 1 to 3
`a[:end]`	`a[:3]`	From 0 to 2
`a[start:]`	`a[2:]`	From 2 to end
`a[::step]`	`a[::2]`	Every 2nd element
`a[::-1]`	Reverse array
`a[row, col]`	`a[1,2]`	Element at row 1 col 2
`a[rows, cols]`	`a[0:2, 1:3]`	Sub-matrix

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How to use NumPy Array Slicing?

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1. Slicing a 1-D Array

Example:

a) Basic slicing

b) Without start

c) Without end

d) With step

e) Reverse slicing

2. Slicing a 2-D Array

a) Slice specific row

b) Slice specific column

c) Slice a sub-matrix

3. Slicing With Steps (2D)

Example: Every 2nd row and column

4. Slicing Higher-Dimensional Arrays (3D)

Summary Cheatsheet