如何将csv文件中的字符串转换为python中的列表

Question

I have a CSV file that contains matrix:

1,9,5,78
4.9,0,24,7
6,2,3,8
10,21.4,8,7

I want to create a function that returns list of lists:

[[1.0,9.0,5.0,78.0],[4.9,0.0,24.0,7.0],[6.0,2.0,3.0,8.0],[10.0,21.4,8.0,7.0]]

this is my attempt:

fileaname=".csv"
def get_csv_matrix(fileaname):
    mat=open(fileaname,'r')
    mat_list=[]
    for line in mat:
        line=line.strip()
        mat_line=[line]
        mat_list.append(mat_line)
return mat_list

but I get list of lists with one string:

[['1,9,5,78'], ['4.9,0,24,7'], ['6,2,3,8'], ['10,21.4,8,7']]

how can i turn the lists of strings to lists of floats?

Answer 1

mat_line = [line]

This line just takes the line as a single string and makes it into a one element list. If you want to separate it by commas, instead do:

mat_line = line.split(',')

If you want to also turn them into numbers, you'll have to do:

mat_line = [float(i) for i in line.split(',')]

Answer 2

I find it easier to read a list comprehension than a for loop.

def get_csv_matrix(filename):
    with open(filename) as input_file:
        return [[float(i) for i in line.split(',')] for line in input_file]

print (get_csv_matrix("data.csv"))

The above function opens a file (I use with to avoid leaking open file descriptors), iterates over the lines, splits each line, and converts each item into a floating-point number.

Answer 3

Try

fileaname=".csv"
def get_csv_matrix(fileaname):
    mat=open(fileaname,'r')
    mat_list=[]
    for line in mat:
        line=line.strip()
        mat_line=line.split(",")
        for i in mat_line:
            i_position = line.index(i)
            line[i_position] = float(i)
        mat_list.append(mat_line)
    return mat_list

If any object in mat_line isn't an integer, you will come up with an error, so I suggest you create a validation method to be absolutely sure that it is an integer.