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Polynomial Feature Expansion

Implement polynomial feature expansion for a single-feature input.

Given a list of values $x$ and a degree $d$ , create the expanded feature matrix where each row contains $[x_i, x_i^2, x_i^3, ..., x_i^d]$ .

For example, if $x = [2, 3]$ and degree $= 3$ , the output matrix is: $\begin{bmatrix} 2 & 4 & 8 \\ 3 & 9 & 27 \end{bmatrix}$

Return the feature matrix as a 2D list, with each value rounded to 4 decimal places.

Input:

x = [2, 3]
degree = 3

Output:

[[2, 4, 8], [3, 9, 27]]

Reasoning:

The input list $x = [2, 3]$ and degree $d = 3$ are given, and we need to create the expanded feature matrix.
For each value $x_i$ in the list, we calculate the powers of $x_i$ from $1$ to $d$ : $x_i^1, x_i^2, ..., x_i^d$ . For $x_1 = 2$ , this gives us $2^1 = 2$ , $2^2 = 4$ , and $2^3 = 8$ .
We repeat this process for $x_2 = 3$ : $3^1 = 3$ , $3^2 = 9$ , and $3^3 = 27$ .
The results are combined into a 2D list, where each row corresponds to the expanded features for each input value: $[[2, 4, 8], [3, 9, 27]]$ .

Editor

Python 3.13.1

0/0

Run code to see test results.

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