awk append lines if certain field matches - awk

Question

I'm an absolute beginner to awk and would like some help with this.
I have this data:
FOO|BAR|1234|A|B|C|D|
FOO|BAR|1234|E|F|G|H|
FOO|BAR|5678|I|J|K|L|
FOO|BAR|5678|M|N|O|P|
FOO|BAR|5678|Q|R|S|T|
Desired output:
FOO|BAR|1234|A|B|C|D|E|F|G|H|
FOO|BAR|5678|I|J|K|L|M|N|O|P|Q|R|S|T|
Basically I have to append some fields to the lines where column 3 matches.
Appreciate any responses, thanks a lot!

Answer 1

Another way:
awk -F"|" '$3 in a{
a[$3]=a[$3]"|"$4"|"$5"|"$6"|"$7;
next
}
{ a[$3]=$0
}
END {
for ( i in a) {
print a[i]
}
}'

Answer 2

$ awk -f chain.awk < data
FOO|BAR|1234|A|B|C|D|E|F|G|H|
FOO|BAR|5678|I|J|K|L|M|N|O|P|Q|R|S|T|
$ cat chain.awk
BEGIN {FS = "|"}
$3==old {for(i = 4; i <= NF; i++) saved = saved (i>4?"|":"") $i}
$3!=old {if(old) print saved ; saved = $0 ; old = $3}
END {print saved}
$
BEGIN we set the field separator
$3==old we append the fields $4 ... $NF to the saved data, joining the fields with | except for the first one (note that there is a last, null field)
$3!=old we print the saved data (except for the first record, when old is false) and we restart the mechanism
END we still have saved data in our belly, we have to print it