列データを行データに転換

Awk: transpose – separator in the end – StackOverflow

%%bash
time {
echo """45
78
45""" |
awk 'BEGIN{RS="";OFS=","}{$1=$1}1'
}

45,78,45

real    0m0.004s
user    0m0.003s
sys 0m0.002s

%%bash
time {
echo """45
78
45""" | paste -s -d,
}

45,78,45

real    0m0.004s
user    0m0.002s
sys 0m0.003s

%%bash
time {
echo """45
78
45""" | tr '\n' ',' | sed 's/,$//'
}

45,78,45
real    0m0.005s
user    0m0.003s
sys 0m0.006s

import re


strings = """45
78
45"""

re.sub(r'(?<=\d)\n(?=\d+)', ',', strings)

'45,78,45'