CODEWITHSUNDEEP
pythonregex
Lucas
Lucas

Reputation: 159

Python regular expression grabbing a middle number

Say I have a string that looks like this "53.4 -63.2 433.2" three separate numbers. How do I get the middle one only and so I dont ignore a minus if the number is negative?

Ive managed to gather to use (\d+) to group the numbers and to grab more than one..But I dont know what to add? IVe looked at similar questions but I guess I could not find a similar enough case to what I am trying to do

Upvotes: 0

Views: 908

Answers (7)

Martin Evans
Martin Evans

Reputation: 46759

If you are reading from a file, something like the following could be used:

import csv

reader = csv.reader(open("numbers.txt", "rb"), delimiter=" ")

for row in reader:
    if len(row) == 3:
        print row[1]

As mentioned, use of a regular expression seems like overkill.

Upvotes: 0

Avinash Raj
Avinash Raj

Reputation: 174706

You may use re module.

re.search(r'(?s)^\S+\s+(\S+)', stri).group(1)

Example:

>>> import re
>>> s = ["""53.4
-63.2 433.2""", """53.4 -63.2 433.2""", """53.4 -63.2
 433.2"""]
>>> [re.search(r'(?s)^\S+\s+(\S+)', i).group(1) for i in s]
['-63.2', '-63.2', '-63.2']

Upvotes: 0

Open AI - Opting Out
Open AI - Opting Out

Reputation: 24133

def middle_floats(filename):
    with open(filename) as lines:
        for line in lines:
            yield line.split()[1]

Upvotes: 0

albert
albert

Reputation: 8593

Aussuming your data has the form of the sample multiline_string you can iterate through the string line by line by providing an iterator and split() each line into several groups. If there are exact three groups take the middle one and cast the string into a float. Pass the extracted number (which is a float) to abs() to get the absolute value:

#!/usr/bin/env python3
# coding: utf-8

multiline_string = """
123 -456 789
101 102 103
35.7 -43.8 21.8  
10. 10.2 10.3
"""

for line in iter(multiline_string.splitlines()):
    groups = line.split()
    if len(groups) == 3:
        number = abs(float(line.split()[1]))
        print(number)

Upvotes: 0

Luc DUZAN
Luc DUZAN

Reputation: 1319

Contrary to other response, I am going to give you the regular expression way that will only match for line of three number.

I will do it this way : catch three number which could have an optional negate (?-) and which could have optional dot with digit after (.?)\d+, I will put a group mark on the second to retrieve it (-?\d+.?\d+). And I will able those number to be separated by a random number of space \s+.

import re
m = re.search(r"-?\d+\.?\d+\s+(-?\d+\.?\d+)\s+-?\d+\.?\d+", "53.4 -63.2 433.2")
print(re.group(1))

If you have difficulty understanding my regexp, you should copy it in https://regex101.com/#python : it will give an explanation for everything.

You should also take a look at Python re module documentation : https://docs.python.org/2/library/re.html

Upvotes: 2

user4097444
user4097444

Reputation:

I hope this will help:

str_num =  "53.4 -63.2 433.2"
list_num = str_num.split("\t")

# Now print the middle item by using lenght of list divided by 2.
middle = list_num[len(list_num)/2]

This will work for list of any lenght. So, you don't have to hardcode the index.

Upvotes: 0

Rob Foley
Rob Foley

Reputation: 581

If there will always be 3 numbers per line, separated with spaces, then regex is a bit overkill. Something like this should suffice:

numbers = []
for line in infile:
    numbers.append(line.split()[1])

Upvotes: 0

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