Merge group numbers and add a column containing group names

I have a file in the following format. Groups of data merge together and the group number is indicated above each group.

1
adrf
dfgr
dfg
2
dfgr
dfgr
3
dfef
dfr
fd
4
fgrt
fgr
fgg
5
fgrt
fgr
fgr
.
.
.
.
50
dfgr
dfd
fdd
fdf
dfdg

I wanted to add another column (separated by tab) such that the file looks like:

adrf 1
dfgr 1
dfg 1
dfgr 2
dfgr 2
dfef 3
dfr 3
fd 3
fgrt 4
fgr 4
fgg 4
fgrt 5
fgr 5
fgr 5
.
.
.
.
50
dfgr 50
dfd 50
fdd 50
fdf 50
dfdg 50

Basically add a column that contains the number of each group and delete the group heading and merge.

Is there an efficient way using shell scripting to do it. I have 1000's of such small groups to manipulate.

Please let me know.

awk '/^[0-9]/ { N = $1; next } { print $1 "\t" N }' file1

adrf    1
dfgr    1
dfg     1
dfgr    2
dfgr    2
dfef    3
dfr     3
fd      3
fgrt    4
fgr     4
fgg     4
fgrt    5
fgr     5
fgr     5

perl:

while(<DATA>){
	chomp;
	if(/^([0-9]+)$/){
		$id=$1;
		next;
	}
	print $_," ",$id,"\n";
}
__DATA__
1
adrf
dfgr
dfg
2
dfgr
dfgr
3
dfef
dfr
fd
4
fgrt
fgr
fgg
5
fgrt
fgr
fgr

bash:

#!/bin/bash

file=/home/mo/scripts/group.txt

for line in $(cat $file); do
        if [[ $line == [0-9]* ]]; then
                symbol=$line
        else
                echo "$line $symbol"
        fi
done