将列表元素转换为数字

Question

There is a csv file with the below three lines.

8.84,17.22,13.22,3.84
3.99,11.73,19.66,1.27
16.14,18.72,7.43,11.09

I am writing a function which reads lines from a file and appends it to an empty list so that I can use that list for computing mean.

Below is the code I wrote:

def my_calc(filename):
    mydata = []
    for line in open(filename).readlines():
         mydata = mydata + line.strip().split(',')
    return mydata

Here is the output:

['"8.84', '17.22', '13.22', '3.84"', '"3.99', '11.73', '19.66', '1.27"', '"16.14', '18.72', '7.43', '11.09"']

The list elements are strings. How can I convert these to float numbers?

I tried map() but I am getting an error message 'could not convert string to float '.

Thank you!

Answer 1

Try this :

a = ['"8.84', '17.22', '13.22', '3.84"', '"3.99', '11.73', '19.66', '1.27"', '"16.14', '18.72', '7.43', '11.09"']
result = map(float, map(lambda x : x.strip('"'), a))

Output :

[8.84, 17.22, 13.22, 3.84, 3.99, 11.73, 19.66, 1.27, 16.14, 18.72, 7.43, 11.09]

In case of python3, do this :

result = list(map(float, map(lambda x : x.strip('"'), a)))

Answer 2

You can modify your function to append items as float only:

import re

def my_calc(filename):
    mydata = []
    for line in open(filename).readlines():
        numbers = map(lambda x: float(x), re.sub("['\"]","",line).split(','))
        mydata.append(numbers)
    return mydata

That should give output:

[[8.84, 17.22, 13.22, 3.84], [3.99, 11.73, 19.66, 1.27], [16.14, 18.72, 7.43, 11.09]]

Answer 3

list = ["8.84,17.22,13.22,3.84", "3.99,11.73,19.66,1.27", "3.99,11.73,19.66,1.27"]
result = []
for el in list:
  strings = el.split(',')
  floats = []
  for el_s in strings:
    floats.append(float(el_s))
  result.append(floats)

print(result, type(result[0][0]))

https://repl.it/G9oO I'm bad with lambdas, this can help you.

Answer 4

Thank you for posting your answers!

Here's my solution. I took bits and pieces of all your solutions to come up with this one.

# Workable solution
mylist = []
a = ['"8.84', '17.22', '13.22', '3.84"', '"3.99', '11.73', '19.66', '1.27"', '"16.14', '18.72', '7.43', '11.09"']
for i in range(0,len(a)):
    mylist.append(a[i].lstrip('"').rstrip('"'))
    mylist = [float(x) for x in mylist]
print(mylist)

Output:

[8.84, 17.22, 13.22, 3.84, 3.99, 11.73, 19.66, 1.27, 16.14, 18.72, 7.43, 11.09]