如何将列表列表中的所有字符串转换为浮点数

Question

I've used this code to open a excel file, to create lists of each line of the excel file:

import csv
with open("csvfile.csv", "rb") as f:
    lines = list(csv.reader(f))

>>> lines
[['0', '23.345', '-122.456'], ['1', '12.546', '-118.987'] ['2', '67.435', '-104.112']]

I do want to keep the lists of each line of the excel file in a bigger list, but I want each element to be floats rather than strings. What alteration would I have to make?

ie [[0, 23.345, -122.456], [1, 12.546, -118.987], [2, 67.435, -104.112]]

Answer 1

You may use nested list comprehension on your list of lists as:

>>> my_list = [['0', '23.345', '-122.456'], ['1', '12.546', '-118.987'], ['2', '67.435', '-104.112']]

>>> [[float(i) for i in sub_list] for sub_list in my_list]
[[0.0, 23.345, -122.456], [1.0, 12.546, -118.987], [2.0, 67.435, -104.112]]

Answer 2

Use map in a list-comprehension while reading the file.

import csv

with open("csvfile.csv", "rb") as f:
    lines = [map(float, line) for line in csv.reader(f)]

Saves you creating a list twice (reading, converting)

Answer 3

You can use map() with a list comprehension :

[map(float, sub_list) for sub_list in my_list]

Output:

>>> [map(float, sub_list) for sub_list in my_list]
[[0.0, 23.345, -122.456], [1.0, 12.546, -118.987], [2.0, 67.435, -104.112]]

Answer 4

Change:

lines = list(csv.reader(f))

into:

lines = [[float(x) for x in line] for line in csv.reader(f)]

ie:

import csv
    with open("csvfile.csv", "rb") as f:
        lines =  [[float(x) for x in line] for line in csv.reader(f)]