Separate comma delimited cells to new rows with shell script - linux

Question

I have a table with comma delimited columns and I want to separate the comma delimited values in my specified column to new rows. For example, the given table is
Name Start Name2
A 1,2 X,a
B 5 Y,b
C 6,7,8 Z,c
And I need to separate the comma delimited values in column 2 to get the table below
Name Start Name2
A 1 X,a
A 2 X,a
B 5 Y,b
C 6 Z,c
C 7 Z,c
C 8 Z,c
I am wondering if there is any solution with shell script, so that I can create a workflow pipe.
Note: the original table may contain more than 3 columns.

Answer 1

Assuming the format of your input and output does not change:
awk 'BEGIN{FS="[ ,]"} {print $1, $2, $NF; print $1, $3, $NF}' input_file
Input:
input_file:
A 1,2 X
B 5,6 Y
Output:
A 1 X
A 2 X
B 5 Y
B 6 Y
Explanation:
awk: invoke awk, a tool for manipulating lines (records) and fields
'...': content enclosed by single-quotes are supplied to awk as instructions
'BEGIN{FS="[ ,]"}: before reading any lines, tell awk to use both space and comma as delimiters; FS stands for Field Separator.
{print $1, $2, $NF; print $1, $3, $NF}: For each input line read, print the 1st, 2nd and last field on one line, and then print the 1st, 3rd, and last field on the next line. NF stands for Number of Fields, so $NF is the last field.
input_file: supply the name of the input file to awk as an argument.
In response to updated input format:
awk 'BEGIN{FS="[ ,]"} {print $1, $2, $4","$5; print $1, $3, $4","$5}' input_file

Answer 2

After Runner's modification of the original question another approach might look like this:
#!/bin/sh
# Usage $0 <file> <column>
#
FILE="${1}"
COL="${2}"
# tokens separated by linebreaks
IFS="
"
for LINE in `cat ${FILE}`; do
# get number of columns
COLS="`echo ${LINE} | awk '{print NF}'`"
# get actual field by COL, this contains the keys to be splitted into individual lines
# replace comma with newline to "reuse" newline field separator in IFS
KEYS="`echo ${LINE} | cut -d' ' -f${COL}-${COL} | tr ',' '\n'`"
COLB=$(( ${COL} - 1 ))
COLA=$(( ${COL} + 1 ))
# get text from columns before and after actual field
if [ ${COLB} -gt 0 ]; then
BEFORE="`echo ${LINE} | cut -d' ' -f1-${COLB}` "
else
BEFORE=""
fi
AFTER=" `echo ${LINE} | cut -d' ' -f${COLA}-`"
# echo "-A: $COLA ($AFTER) | B: $COLB ($BEFORE)-"
# iterate keys and re-build original line
for KEY in ${KEYS}; do
echo "${BEFORE}${KEY}${AFTER}"
done
done
With this shell file you might do what you want. This will split column 2 into multiple lines.
./script.sh input.txt 2
If you'd like to pass inputs though standard input using pipes (e.g. to split multiple columns in one go) you could change the 6. line to:
if [ "${1}" == "-" ]; then
FILE="/dev/stdin"
else
FILE="${1}"
fi
And run it this way:
./script.sh input.txt 1 | ./script.sh - 2 | ./script.sh - 3
Note that cut is very sensitiv about the field separators. Soif the line starts with a space character, column 1 would be "" (empty). If the fields were separated by amixture of spaces and tabs this script would have other issues too. In this case (as explained above) filtering the input resource (so that fields are only separated by one space character) should do it. If this is not possible or the data in each column contains space characters too, the script might get more complicated.