Python: How to join string elements in list with complex notation

Question

Edited to show more accurate strings

I have a long list with the following grouping structure. I am showing just two groups, but in reality there are 300. The strings can be any random collection of numbers and letters:

["['P431', 'N7260', 'K492'], ['R109', 'T075X9A'], ['U8154', 'C861']",
 "['R878X8', 'T61'], ['F6332', 'Q7979'], ['L520'], ['B7939', 'K5132']"]

For each group in the list, I want the final output to look like the following:

[['P431 N7260 K492 R109 T075X9A', 'U8154 C861'],
['R878X8 T61 F6332 Q7979 L520', 'B7939 K5132']]

So for each group in the list, I want to join all of the elements in every sub-list except the last sub-list, then separately join all of the elements in the last sub-list, and finally add these both together into a single sub-list, each of which will now have just two elements. Thank you in advance as I am a beginner.

Asked By: JTA1618

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Source

Answer 1

I’m assuming you’have some typos in your string (missing '). You can try:

from ast import literal_eval

l = [
    "['cat', 'dog', 'mouse'], ['squirrel', 'lion'], ['fox', 'rabbit']",
    "['chipmunk', 'lion'], ['hyena', 'wolf'], ['owl', 'sloth']",
]

l = [
    [" ".join(w for ll in subl for w in ll), " ".join(last)]
    for s in l
    for *subl, last in [literal_eval(s)]
]

print(l)

Prints:

[
  ['cat dog mouse squirrel lion', 'fox rabbit'], 
  ['chipmunk lion hyena wolf', 'owl sloth']
]

Answered By: Andrej Kesely

Answer 2

use ast.literal_eval for construct list from string, then join with space all except the last and then union all together

import ast
result = []

for group in data:
    subgroups = ast.literal_eval(group)

    # join all except last
    combined = [' '.join(subgroup) for subgroup in subgroups[:-1]]
    # last append   
    last_subgroup = ' '.join(subgroups[-1])

    
    result.append([' '.join(combined), last_subgroup])

print(result)

Answered By: Anna Andreeva Rogotulka

Answer 3

You can try this:

from ast import literal_eval

example=[
    "['P431', 'N7260', 'K492'], ['R109', 'T075X9A'], ['U8154', 'C861']",
    "['R878X8', 'T61'], ['F6332', 'Q7979'], ['L520'], ['B7939', 'K5132']",
    "['a','b','c'], 'not a list'"
]

for st in example:
    *first_grp,last=literal_eval(st)
    if any(not isinstance(s, list) for s in (first_grp, last)):
        continue 
    print([" ".join([e for r in first_grp for e in r]), " ".join(last)])

Prints:

['P431 N7260 K492 R109 T075X9A', 'U8154 C861']
['R878X8 T61 F6332 Q7979 L520', 'B7939 K5132']

This is similar to Andrej Kesely solution but may overcome the ‘random strings’ you describe with a type check.

Answered By: dawg

Python: How to join string elements in list with complex notation

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