如何用for循环读取含数值的TXT文件并转换为N×N矩阵

我正在计算城市间的距离，文本文件存储了所有待访问城市间的距离。若有N个城市，文件中则是一个N×N的浮点数数组，其中元素(i,j)代表城市i到城市j的距离。我已创建好全0的N×N矩阵，且读取了文件第一行，如何用for循环将文件内容转换为目标N×N矩阵？

示例文件内容 #

small_distances.txt的内容如下：

0.0 2.0 2.23606797749979 4.47213595499958 5.385164807134504
2.0 0.0 2.23606797749979 4.0 3.605551275463989
2.23606797749979 2.23606797749979 0.0 2.23606797749979 4.0
4.47213595499958 4.0 2.23606797749979 0.0 3.605551275463989
5.385164807134504 3.605551275463989 4.0 3.605551275463989 0.0

现有代码 #

def create_2_list(rows,columns): 
    the_2d_list = []
    for i in range(rows):
        current_row = []
        for j in range(columns):
            current_row.append(0)
        the_2d_list.append(current_row)
    return the_2d_list

def print_2d_list(the_list):
    for i in range(len(the_list)):
        for j in range(len(the_list[i])):
            print(the_list[i][j], end=' ')
        print()

def read_line_in_txt(file):
    file = open(filename,'r')
    line = file.readline()
    t = line.split()

    return t

filename = 'small_distances.txt'
the_file = open(filename,'r')
the_data = the_file.readlines()

the_file.close()

n_cities = len(the_data)

distances = create_2_list(n_cities,n_cities)
print_2d_list(distances)
print('---------------------------')
line = read_line_in_txt(the_data)
print(line)
 print('---------------------------')

预期输出 #

0.0 2.0 2.23606797749979 4.47213595499958 5.385164807134504 
2.0 0.0 2.23606797749979 4.0 3.605551275463989 
2.23606797749979 2.23606797749979 0.0 2.23606797749979 4.0 
4.47213595499958 4.0 2.23606797749979 0.0 3.605551275463989 
5.385164807134504 3.605551275463989 4.0 3.605551275463989 0.0

文本行拆分示例 #

通过拆分文本行可得到城市距离列表：

# 文本文件第一行
t = '0.0 2.0 2.23606797749979 4.47213595499958 5.385164807134504'
t.split()
# 输出结果：
# ['0.0', '2.0', '2.23606797749979', '4.47213595499958', '5.385164807134504']
# 对应城市1到城市2、3、4、5的距离

len(t.split())
# 输出结果：5
# 利用这个信息可以通过嵌套for循环构建距离矩阵

解决方案 #

要将文件内容填充到全0矩阵中，只需遍历已读取的每一行数据，拆分后转换为浮点数，再通过for循环逐个赋值到矩阵对应位置即可。同时需要修正现有代码中read_line_in_txt函数的错误（该函数参数未被使用，且重复打开文件，实际无需单独定义此函数）。修改后的完整代码如下：

def create_2_list(rows, columns): 
    the_2d_list = []
    for i in range(rows):
        current_row = []
        for j in range(columns):
            current_row.append(0)
        the_2d_list.append(current_row)
    return the_2d_list

def print_2d_list(the_list):
    for i in range(len(the_list)):
        for j in range(len(the_list[i])):
            print(the_list[i][j], end=' ')
        print()

filename = 'small_distances.txt'
the_file = open(filename, 'r')
the_data = the_file.readlines()
the_file.close()

n_cities = len(the_data)
distances = create_2_list(n_cities, n_cities)

# 用for循环填充矩阵
for i in range(n_cities):
    # 去除行尾换行符并拆分字符串
    row_data = the_data[i].strip().split()
    for j in range(n_cities):
        # 将字符串转换为浮点数后赋值
        distances[i][j] = float(row_data[j])

# 打印结果
print_2d_list(distances)

代码说明 #

1. 外层for循环遍历每一行数据，对应矩阵的行索引i
2. 对每一行先去除换行符，再用split()拆分得到距离字符串列表
3. 内层for循环遍历每个距离值，对应矩阵的列索引j
4. 将字符串转换为浮点数，赋值到distances[i][j]位置

内容的提问来源于stack exchange，提问作者John