如何读取文件并将数据存储到列表中

Question

If I have a file in this format:

1 2 3 4 5
6 7 8 9 10

What is the correct way to read the file and store each digit into a list in Python?

x_table = []
for eachLine in filename_1:
#Set up temp variable
    x_table.append([])
    tmpStr = ''
#Loop through each character in the line
    for char in eachLine:
    #Check whether the char is a number
        if char.isdigit():
            tmpStr += char
        elif char == ' ' and tmpStr != '':
            x_table[eachLine].append(int(char))

I got this error:

type: list indices must be integers, not str.

Answer 1

Read each line and use split() to separate the digits into separate numbers:

mat = []
for line in open('file.txt').readlines():
    mat.append(line.split())

After that, if you want, you can validate if all the lines have the same number of elements.

Answer 2

eachLine is a string (more specifically a line in your document) so you can't use that as an index for your x_table array of arrays.

You could just keep a running count:

x_table = []
idx = 0
for eachLine in filename_1:
    # ...
    x_table[idx].append(int(char))
    idx += 1

EDIT: or, if you want to go with the approach elias suggested (see below,) you can use a list comprehension to prune the elements that are not numbers:

raw_mat = []
f = open('file.txt')
for line in f.readlines():
    raw_mat.append(line.split())
f.close()

mat = []
for row in raw_mat:
    mat.append([i for i in row if i.isdigit()])

Answer 3

If you need numbers processing this function will work: http://docs.scipy.org/doc/numpy/reference/generated/numpy.loadtxt.html Unless you need to alter the array-of-arrays (data is loaded into a numpy.ndarray, which is efficient if you need numbers and math processing).

Another solution:

If you need an array-of-arrays and you don't want to change your core code, note that each element in the for ... in ... is not the index position, but the actual element.

to get the index position do: for i, v in enumerate(filename_1):

And even then, if filename_1 is a string, it's not ok. you should specify a file object there (it's iterable, and line by line).

For each line (eachLine) you could append to x_table the following code:

x_table.append([int(s) for s in eachLine.split()])
#eachLine.split() will break eachLine by whitespace-strings.

remember to capture exceptions here.

full code:

x_table = []
for eachLine in open(filename_1, "r"):
    x_table.append([int(k) for k in eachLine.split()])

full code for numpy version:

import numpy
x_table = numpy.loadtxt(open(filename_1,"r").read())

remember to capture exceptions in both codes.

Answer 4

x_table = []
for line in filename_1:
    numbers = map(int, line.split(' '))
    x_table.append(numbers)

Taken care of:

• multi-digit numbers
• negative numbers (the minus sign)

Answer 5

You can use regular expression. This example will parse decimals, negatives, and exclude text.

"""Contents of test.txt:
1 2 3.14 4 5 0 text
6 7 -8 9 10 -99.99
some other text
1.0 0.5
"""

import re

filename_1 = open("test.txt", 'r')
values = re.findall(r"-*\d+\.*\d*", filename_1.read())

print values

Note that this will return a list. You can then convert the values to int or float.

Answer 6

Simple:

file = open("myfile.dat", "r")

matrix = []
for line in file:
    matrix.append(line.split()[:])