How to convert a string containing several float numbers into an array of float in Python?

Question

I have a text file which contains float characters line by line as

    15.723
    17.567

I tried reading the file and after doing this

with open('<path_to_file>/writefile.txt', 'r') as fin:
    data_read = fin.read()

When I print data_read, I get

'15.723\n17.567\n'

Now I need to save this string into an array containg

float_array[0]=15.723
float_array[1]=17.567

How do I do the conversion?

I tried

print(float(data_read))
res = data_read.astype(float)
print(res)

And I got

ValueError: could not convert string to float: '15.723\n17.567\n'

What am I doing wrong here?

I am expecting something like float_array[0]=15.723 float_array[1]=17.567

@PM77-1 Ok... What and how should I split? The '\n' delimiter serves as saperating each variable. How do I differentiate each variable after splitting? — usrp_hacker
– usrp_hacker, Commented Sep 9, 2022 at 13:59
@MadPhysicist array list doesn't matter. As long as I can access the variable as float — usrp_hacker
– usrp_hacker, Commented Sep 9, 2022 at 13:59
@usrp_hacker. It does matter, because those two words mean different things in python. If you're not sure, you want a list. — Mad Physicist
– Mad Physicist, Commented Sep 9, 2022 at 14:00
python-reference.readthedocs.io/en/latest/docs/str/split.html — PM 77-1
– PM 77-1, Commented Sep 9, 2022 at 14:01

Psytho · Accepted Answer · 2022-09-09 14:02:42Z

1

You can read the file directly into a list of strings (using readlines()) and then convert every line to float. So you don't have to use split()

with open('<path_to_file>/writefile.txt', 'r') as fin:
    data_read = fin.readlines()
numbers = list(map(float, data_read))

answered Sep 9, 2022 at 14:02

Psytho

3,4142 gold badges22 silver badges28 bronze badges

Sign up to request clarification or add additional context in comments.

4 Comments

usrp_hacker Over a year ago

ValueError: could not convert string to float: '20,807\n' I am getting such error. I am living in Europe, so the , is used as floating point here

Psytho Over a year ago

why then you have . in you sample data and not ,? But anyway it is another problem, unrelated to your inital question.

usrp_hacker Over a year ago

I did data_read = data_read.replace(',', '.'). In Europe, the , is used as floating point. I wasn't sure if that is causing any issue so I did this.

usrp_hacker Over a year ago

It works. My bad. There was a EOL at the end of the file which was preventing the numbers from getting converted to float. It's all good now

Mad Physicist · Accepted Answer · 2022-09-09 16:00:17Z

0

First split your string into individual numbers:

list_of_strings = data_read.split()

Now you can apply float to each element:

list_of_floats = [float(x) for x in list_of_strings if x]

The check if x discards the last empty element if your file ends with a newline. If it doesn't, you can do

list_of_floats = list(map(float, list_of_strings))

Or you can strip the data first:

list_of_strings = data_read.strip().split()

edited Sep 9, 2022 at 16:00

answered Sep 9, 2022 at 13:56

Mad Physicist

116k29 gold badges202 silver badges292 bronze badges

4 Comments

alec_djinn Over a year ago

Better be explicit here and pass the splitting parameter data_read.split('\n')

Mad Physicist Over a year ago

@alec_djinn. Not passing it in will automatically strip off unnecessary whitespace too, which is nice.

usrp_hacker Over a year ago

I tried but I am getting Traceback (most recent call last): File "<path>\PycharmProjects\pythonProject\main.py", line 17, in <module> list_of_floats = list(map(float, list_of_strings)) ValueError: could not convert string to float: ''

Mad Physicist Over a year ago

@usrp_hacker. Good call. Updated

Collectives™ on Stack Overflow

How to convert a string containing several float numbers into an array of float in Python?

2 Answers 2

4 Comments

4 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

4 Comments

4 Comments

Your Answer

Sign up or log in

Post as a guest

Related