Extract data from string in python

Question

I have a .csv file with data constructed as [datetime, "(data1, data2)"] in rows and I have managed to import the data into python as time and temp, the problem I am facing is how do I seperate the temp string into two new_temp columns in float format to use for plotting later on?

My code so far is:

import csv
import matplotlib.dates as dates

def getColumn(filename, column):
    results = csv.reader(open('logfile.csv'), delimiter = ",")
    return [result[column] for result in results]
time = getColumn("logfile.csv",0)
temp = getColumn("logfile.csv",1)
new_time = dates.datestr2num(time)
new_temp = [???]

When I print temp I get ['(0.0, 0.0)', '(64.4164, 66.2503)', '(63.4768, 65.4108)', '(62.7148, 64.6278)', '(62.0408, 63.9625)', '(61.456, 63.2638)', '(61.0234, 62.837)', '(60.6823, 62.317)',...etc]

If anyone can help me then thanks in advance.

As a side note, you should read the CSV only once and then extract the columns. Currently you read the whole file over and over. — CodeMonkey
– CodeMonkey, Commented Jul 11, 2016 at 12:52
I checket that solution and wrote make_tuple(temp) and get the error: ValueError: malformed string. And i also tried the tuple(int(x) for x in temp[1:-1].split(',')) and get the error: AttributeError: 'list' object has no attribute 'split' — Gísli Trausti Jóhannesson
– Gísli Trausti Jóhannesson, Commented Jul 11, 2016 at 13:06

Ohumeronen · Accepted Answer · 2016-07-12 09:17:02Z

1

You may use this code:

import re
string = "['(0.0, 0.0)', '(64.4164, 66.2503)', '(63.4768, 65.4108)', '(62.7148, 64.6278)', '(62.0408, 63.9625)', '(61.456, 63.2638)', '(61.0234, 62.837)', '(60.6823, 62.317)']"
data = re.findall('[+-]?\d+\.\d+e?[+-]?\d*', string)
data = zip(data[0::2], data[1::2])
print [float(d[0]) for d in data]
print [float(d[1]) for d in data]

edited Jul 12, 2016 at 9:17

answered Jul 11, 2016 at 12:52

Ohumeronen

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7 Comments

CodeMonkey Over a year ago

This will fail if you have some differently formatted floats (e.g. 5.2456e10). Better use Python's built in parser for evaluating Python expressions in strings as suggested in the comments.

Ohumeronen Over a year ago

No special format was mentioned but thanks for the suggestion.

CodeMonkey Over a year ago

Does it work with 5.2456e-10, 5.2456e+9, -5.2456e-10, .1, 1.?

Ohumeronen Over a year ago

Yes, now it does, but I am sure you will find another case ;-) Deutsche Korrektheit was?

Ohumeronen Over a year ago

I found that the suggestion of user3387223 was quite important so I improved the solution again to allow negative values.

|

Community · Accepted Answer · 2017-05-23 12:22:30Z

1

Going from the answer in Parse a tuple from a string?

from ast import literal_eval as make_tuple
temp = ['(0.0, 0.0)', '(64.4164, 66.2503)', '(63.4768, 65.4108)', '(62.7148, 64.6278)', '(62.0408, 63.9625)', '(61.456, 63.2638)', '(61.0234, 62.837)', '(60.6823, 62.317)']

tuples = [make_tuple(stringtuple) for stringtuple in temp]

and you have an array of tuples of doubles.

I undeleted the post and made it a full answer, because apparently it wasn't clear enough to reference the other post.

edited May 23, 2017 at 12:22

CommunityBot

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answered Jul 11, 2016 at 12:47

CodeMonkey

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1 Comment

Moon Cheesez Over a year ago

If it has already been answered, post it as a comment, not an answer. E.g. Possible duplicate of stackoverflow.com/questions/9763116/parse-a-tuple-from-a-string

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