如何定义二维数组? [英] How to define a two-dimensional array?

问题描述

我想定义一个二维数组，而没有这样的初始化长度:

I want to define a two-dimensional array without an initialized length like this:

Matrix = [][]

但它不起作用...

我已经尝试过下面的代码，但这也是错误的:

I've tried the code below, but it is wrong too:

Matrix = [5][5]

错误:

Traceback ...

IndexError: list index out of range

我怎么了?

推荐答案

从技术上讲，您正在尝试索引未初始化的数组.您必须先使用列表初始化外部列表，然后再添加项目.Python 调用这个列表理解".

You're technically trying to index an uninitialized array. You have to first initialize the outer list with lists before adding items; Python calls this "list comprehension".

# Creates a list containing 5 lists, each of 8 items, all set to 0
w, h = 8, 5;
Matrix = [[0 for x in range(w)] for y in range(h)] 

您现在可以将项目添加到列表中:

Matrix[0][0] = 1
Matrix[6][0] = 3 # error! range... 
Matrix[0][6] = 3 # valid

请注意，矩阵是"y"地址主地址，换句话说，"y索引"位于"x索引"之前.

Note that the matrix is "y" address major, in other words, the "y index" comes before the "x index".

print Matrix[0][0] # prints 1
x, y = 0, 6 
print Matrix[x][y] # prints 3; be careful with indexing! 

尽管您可以根据需要命名它们，但如果您对内部列表和外部列表都使用"x"，并且希望使用非平方矩阵，那么我会以这种方式来避免索引可能引起的混淆.

Although you can name them as you wish, I look at it this way to avoid some confusion that could arise with the indexing, if you use "x" for both the inner and outer lists, and want a non-square Matrix.

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