Regular expression not matching in python

Question

I need to extract a matrix from a string that looks like this (it can be a bigger matrix):

[[13,2,99][-2,3,13][1,3,0][7,77,777]]

I wanted to match all the list looking substrings with a regular expression that i tested on regexr.com that gave me the matches i wanted but not on pythex.org or in my script

Here is a sample code that uses the regex:

import numpy as np
import re
matrix = "[[13,2,99][-2,3,13][1,3,0][7,77,777]]"
l = []
regex = re.compile(r"\[(-?[0-9]+,)+-?[0-9]+]")
for el in re.findall(regex, matrix):
    l.append(np.fromstring(el[1:len(el)-1], dtype=int, sep=",").tolist())
a = np.array(l)

pguardiario · Accepted Answer · 2020-08-17 05:51:21Z

2

You can just jam some commas in there and json.loads it:

json.loads(matrix.replace('][', '],['))

answered Aug 17, 2020 at 5:51

pguardiario

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tripleee · Accepted Answer · 2020-08-17 05:33:20Z

1

The capturing parentheses in your regex causes re.findall to only return the parenthesized submatches. Switching to non-grouping parentheses fixes it.

Python 3.8.2+ (heads/3.8:686d508, Mar 26 2020, 09:32:57) 
[Clang 11.0.3 (clang-1103.0.32.29)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> import re
>>> matrix = "[[13,2,99][-2,3,13][1,3,0][7,77,777]]"
>>> regex = re.compile(r"\[(-?[0-9]+,)+-?[0-9]+]")
>>> re.findall(regex, matrix)
['2,', '3,', '3,', '77,']
>>> regex = re.compile(r"\[(?:-?[0-9]+,)+-?[0-9]+]")
>>> re.findall(regex, matrix)
['[13,2,99]', '[-2,3,13]', '[1,3,0]', '[7,77,777]']

answered Aug 17, 2020 at 5:33

tripleee

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Comments

Rakesh · Accepted Answer · 2020-08-17 05:13:14Z

0

Try Using

import re
import numpy as np

s = "[[13,2,99][-2,3,13][1,3,0][7,77,777]]"
l = []
for i in re.findall(r"(\[.*?\])", s):    # Find everything inside [] brackets. 
    l.append(np.fromstring(i.strip("[]"), dtype=int, sep=","))
    
print(l)

Output:

[array([13,  2, 99]), array([-2,  3, 13]), array([1, 3, 0]), array([  7,  77, 777])]

Without numpy

import re

s = "[[13,2,99][-2,3,13][1,3,0][7,77,777]]"
l = []
for i in re.findall(r"(\[.*?\])", s):
    l.append(list(map(int, i.strip("[]").split(","))))
    
print(l)

Output:

[[13, 2, 99], [-2, 3, 13], [1, 3, 0], [7, 77, 777]]

answered Aug 17, 2020 at 5:13

Rakesh

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Comments

hpaulj · Accepted Answer · 2020-08-17 06:06:12Z

That looks a lot like a list of lists, except for the missing commas. There are various ways massaging and splitting.

In [72]: astr = "[[13,2,99][-2,3,13][1,3,0][7,77,777]]"

get rid of the outer brackets

In [75]: astr.strip('[]')                                                                            
Out[75]: '13,2,99][-2,3,13][1,3,0][7,77,777'

replace the inner ones, and immediately split:

In [76]: astr.strip('[]').replace('][',';').split(';')                                               
Out[76]: ['13,2,99', '-2,3,13', '1,3,0', '7,77,777']

split those inner strings:

In [77]: [sub.split(',') for sub in _]                                                               
Out[77]: [['13', '2', '99'], ['-2', '3', '13'], ['1', '3', '0'], ['7', '77', '777']]

If those sublists are all the same length, and numeric strings, the we can easily make an array from those (with dtype conversion to integer):

In [78]: np.array(_, int)                                                                            
Out[78]: 
array([[ 13,   2,  99],
       [ -2,   3,  13],
       [  1,   3,   0],
       [  7,  77, 777]])

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