How to delete files with spaces 20 days are more senior, having left the last 4 even if they are more senior than 20 days? - bash

Question

How to delete files with spaces 20 days are more senior, having left the last 4 even if they are more senior than 20 days?
Examples of files (where in name 1 - the oldest file):
reckless 1.txt
reckless 2.txt
reckless 3.txt
reckless 4.txt
reckless 5.txt
reckless 6.txt
reckless 7.txt
reckless 8.txt
confidence1.txt
confidence2.txt
confidence3.txt
choke-1.txt
choke-2.txt
choke-3.txt
choke-4.txt
choke-5.txt
choke-6.txt
choke-7.txt
choke-8.txt
choke-9.txt
choke-10.txt
cruel_1_1.txt
cruel_1_2.txt
cruel_1_3.txt
cruel_1_4.txt
cruel_1_5.txt
cruel_2_1.txt
cruel_2_2.txt
cruel_2_3.txt
cruel_2_4.txt
cruel_2_5.txt
cruel_2_6.txt
cruel_2_7.txt
level_1.txt
It turns out that should be deleted from this list:
reckless 1.txt
reckless 2.txt
reckless 3.txt
reckless 4.txt
choke-1.txt
choke-2.txt
choke-3.txt
choke-4.txt
choke-5.txt
choke-10.txt
cruel_1_1.txt
cruel_2_1.txt
cruel_2_2.txt
cruel_2_3.txt
Tried something similar from here: https://stackoverflow.com/a/20034914
But did not understand how to make sorting according to a necessary condition.

Answer 1

Assuming each filename does not contain newline characters,
please try the following:
while IFS= read -r line; do
array=()
while IFS= read -r file; do
[[ $file =~ ^[0-9]+\ (.*)$ ]] && array+=("${BASH_REMATCH[1]}")
done < <(
find . -name "$line*.txt" -type f -mtime +20 -printf "%T# %p\n" | sort
)
for (( i=0; i<${#array[#]}-4; i++ )); do
rm -- "${array[$i]}"
done
done < <(
for f in *.txt; do
[[ $f =~ ^(.*)[-_\ ]+[0-9]+\.txt$ ]] && echo "${BASH_REMATCH[1]}"
done | uniq
)
[Explanations]
First of all, it removes the suffix numbers and extensions from the filenames
to extract a root name as a group name.
Next it finds individual group files which are older than 20 days and
sort them by mtime.
Then it removes older files preserving the latest up to four files in the
group.
If the filenames do contain newline characters, small modification and -z
option support of sort command will answer the requirement.