Reading parameter value from a string-CodePudding

Suppose I have a list of strings that look like:

strings_list = ["a=2,b=3,c=14","a=1,b=4,c=0","a=1,b=80,c=3"]

and I want to iterate over these strings and read off the values of the 'b' parameter. How do I do this? Could you help me filling in the line I wrote as a comment

b_array = []
For s in strings_list:
   # [read off b parameter as a number, call it b_value]
   b_array.append(b_value)

CodePudding user response：

You could just split each string on , and then again on =, saving the values if the first part of the split is b (or some other name):

name = 'b'
result = [int(v[1]) for v in [a.split('=') for s in strings_list for a in s.split(',')] if v[0] == name]

Output (for your sample data):

[3, 4, 80]

You could also take a regex-based approach as shown by @Thefourthbird, and use a defaultdict to extract all values of all parameters at once:

import re
from collections import defaultdict

p = defaultdict(list)
[p[k].append(int(v)) for (k, v) in re.findall('(\w )=(\d )', ','.join(strings_list))]

Output (for your sample data):

{
 'a': [2, 1, 1],
 'b': [3, 4, 80],
 'c': [14, 0, 3]
}

CodePudding user response：

You can capture the digits in a group where the key equals b and use re.findall to get all group matches.

strings_list = ["a=2,b=3,c=14", "a=1,b=4,c=0", "a=1,b=80,c=3"]
b_array = []

[b_array.extend(re.findall(r"\bb=(\d )", s)) for s in strings_list]

print(b_array)

Output

['3', '4', '80']

CodePudding user response：

One possible solution you could do is iterating through the strings_list and for each element, splitting that into a list by commas. Then you would just take the second element, subtract the b=, and convert the remaining number to an integer. The code would look like this:

strings_list = ["a=2,b=3,c=14","a=1,b=4,c=0","a=1,b=80,c=3"]
b_array = []
for s in strings_list:
   splitted = s.split(",")
   b_array.append(int(splitted[1][2:]))
print(b_array) # Returns [3, 4, 80]

If you don't want the b_array to be filled with integers and instead with strings of the b value, simply take out the part where it is converted to an integer.

CodePudding user response：

Use regular expression

import re

strings_list = ["a=2,b=3,c=14","a=1,b=4,c=0","a=1,b=80,c=3"]

b_array = []
for s in strings_list:
    for match in re.finditer(r'([^=,] )=([^,] )', s):
        name, value = match.groups()
        if name == 'b':
            b_array.append(value)

print(b_array)
# ['3', '4', '80']

or a more generic approach, in case you want other parameters than "b":

from collections import defaultdict
import re

strings_list = ["a=2,b=3,c=14","a=1,b=4,c=0","a=1,b=80,c=3"]

parameters = defaultdict(list)

for s in strings_list:
    for match in re.finditer(r'([^=,]) =([^,])', s):
        name, value = match.groups()
        parameters[name]  = [value]


print(parameters['b'])
# ['3', '4', '8']