[Solved] Why does arr[1, :] return a 1D array when arr is a 2D numpy array? — Ans: Because it selects all columns in the 2nd row, reducing dimensions | NumPy

NumPy - Indexing and Slicing

Why does arr[1, :] return a 1D array when arr is a 2D numpy array?

ABecause it selects the entire array

BBecause numpy automatically flattens all arrays

CBecause slicing with ':' returns a scalar

DBecause it selects all columns in the 2nd row, reducing dimensions

Step-by-Step Solution

Solution:

Step 1: Understand slicing in numpy
arr[1, :] selects all columns in row 1.
Step 2: Effect on array dimensions
Selecting a single row with all columns returns a 1D array (row vector), reducing dimension from 2D to 1D.
Final Answer:
Because it selects all columns in the 2nd row, reducing dimensions -> Option D
Quick Check:
Slicing a single row returns 1D array [OK]

Quick Trick: Selecting one row with ':' returns 1D array [OK]

Common Mistakes:

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Why does arr[1, :] return a 1D array when arr is a 2D numpy array?