使用for循环以numpy填充2D矩阵 [英] Filling a 2D matrix in numpy using a for loop

问题描述

我是一个Matlab用户，试图切换到Python.

I'm a Matlab user trying to switch to Python.

使用Numpy，如何在for循环内填充矩阵?

Using Numpy, how do I fill in a matrix inside a for loop?

例如，矩阵有2列，并且for循环的每次迭代都会添加新的一行数据.

For example, the matrix has 2 columns, and each iteration of the for loop adds a new row of data.

在Matlab中，这将是:

In Matlab, this would be:

n = 100;
matrix = nan(n,2); % Pre-allocate matrix
for i = 1:n
    matrix(i,:) = [3*i, i^2];
end

推荐答案

首先，您必须使用

$ pip install numpy

然后以下方法应该起作用

Then the following should work

import numpy as np    
n = 100
matrix = np.zeros((n,2)) # Pre-allocate matrix
for i in range(1,n):
    matrix[i,:] = [3*i, i**2]

一种更快的选择:

col1 = np.arange(3,3*n,3)
col2 = np.arange(1,n)
matrix = np.hstack((col1.reshape(n-1,1), col2.reshape(n-1,1)))

按照Divakar的建议，甚至更快

Even faster, as Divakar suggested

I = np.arange(n)
matrix = np.column_stack((3*I, I**2))

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