Awk array with dynamic indices - arrays

Question

Lets say I have a tab delimited file lookup.txt
070-031 070-291 030-031
1 2 X
2 3 1
3 4 2
4 5 3
5 6 4
6 7 5
7 8 6
8 9 7
And I have the following files with values to lookup from
$cat 030-031.txt
Line1 070-291 4
Line2 070-031 3
$cat 070-031.txt
Line1 030-031 5
Line2 070-291 8
I would like script.awk to return
$script.awk 030-031.txt lookup.txt
Line1 070-291 4 2
Line2 070-031 3 2
and
$script.awk 070-031.txt lookup.txt
Line1 030-031 5 6
Line2 070-291 8 7
The only thing I can think to do is to create two separate expanded lookup.txt eg
$cat lookup_030-031.txt
070-031:1 X
070-031:2 1
070-031:3 2
070-031:4 3
070-031:5 4
070-031:6 5
070-031:7 6
070-031:8 7
070-291:2 X
070-291:3 1
070-291:4 2
070-291:5 3
070-291:6 4
070-291:7 5
070-291:8 6
070-291:9 7
and then
awk 'NR==FNR { a[$1]=$2;next}{print $0,a[$2":"$3]}' lookup_030-031.txt 030-031.txt
This works but I have many more columns and approximately 10000 rows, so i'd rather not have to generate a lookup file for each. Many thanks
AMENDED
Glenn Jackman's answer is a perfect solution to the initial question and his second answer is more efficient. However, I forgot to stipulate that the script should handle duplicates. For instance, it should be able to handle
$cat 030-031
070-031 3
070-031 6
and return BOTH corresponding numbers for the respective file (2 and 5 respectively). Only Glens first answer handles repeated lookups. His second returns the last values found.

Answer 1

OK, I see now. You have to read the lookup file into a big datastructure, then referencing with the individual files is easy.
$ cat script.awk
BEGIN {OFS = "\t"}
NR==1 {
for (i=1; i<=NF; i++)
label[i] = $i
next
}
NR==FNR {
for (i=1; i<=NF; i++)
for (j=1; j<=NF; j++)
if (i != j)
value[label[i],$i,label[j]] = $j
next
}
FNR==1 {
split(FILENAME, a, /\./)
j = a[1]
}
{
$(NF+1) = value[$1,$2,j]
print
}
$ awk -f script.awk lookup.txt 030-031.txt
070-291 4 2
070-031 3 2
$ awk -f script.awk lookup.txt 070-031.txt
030-031 5 6
070-291 8 7
This version is a bit more compact, and passes the filenames in your preferred order:
$ script.awk
BEGIN {OFS = "\t"}
NR==1 {
split(FILENAME, a, /\./)
dest = a[1]
}
NR==FNR {
src[$1]=$2
next
}
FNR==1 {
for (i=1; i<=NF; i++)
col[$i]=i
next
}
{
for (from in src)
if ($col[from] == src[from])
print from, src[from], $col[dest]
}
$ awk -f script.awk 030-031.txt lookup.txt
070-031 3 2
070-291 4 2
$ awk -f script.awk 070-031.txt lookup.txt
030-031 5 6
070-291 8 7

Answer 2

This works but I have many more columns and approximately 10000 rows, so i'd rather not have to generate a lookup file for each.
Your dataset is small enough to where you have the option of keeping the lookups in memory.
In a BEGIN section, read "lookup.txt" into a two-dimension (nested) array so that:
lookup['070-031'][4] = 3
lookup['070-291'][5] = 3
The run through all the data files all at once:
script.awk 070-031.txt 070-291.txt