How to combine two lines that share the same keyword? - bash

Question

lets say I have a file looking somewhat like this:
X NeedThis1 KEYWORD
.
.
NeedThis2 X KEYWORD
And I need to combine the two lines into one like this:
NeedThis2 NeedThis1 KEYWORD
It needs to be done for every line in that file that contains the same KEYWORD but it can't combine two lines that look like this (two X's at the first|second position)
X NeedThis1 KEYWORD
X NeedThis2 KEYWORD
I am considering myself bash-noob so any advice if it can be done with something like awk or sed would be appreciated.

Answer 1

awk '
{if ($1 == "X") end[$3] = $2; else start[$3] = $1}
END {for (kw in start) if (kw in end) print start[kw], end[kw], kw}
' file

Answer 2

Try this:
awk '
$1=="X" {key = $NF; value = $2; next}
$2=="X" && $NF==key {print value, $1, key}' file
Explanation:
When a line where first field is X, store the last field as key and second field as value.
Look for the next line where second field is X and last field matches the key stored from pervious action.
When found, print the value of last matched line along with first field of the current line and the key.
This will most definitely break if your data does not match the sample you have shown (if it has more spaces or fields in between), so feel free to adjust as per your needs.

Answer 3

I won't give you the full answer, but if you have some way to identify "KEYWORD" (not in your problem statement), then use a BASH associative array:
declare -A keys
while IFS= read -u3 -r line
do
set -- $line
eval keyword=\$$#
keys[$keyword]+=${line%$keyword}
done
you'll certainly have to do some more fiddling, but your problem statement is incomplete and some of the work needs to be an exercise for the reader.