sed replace?

Hello. I have this file:

XXXX
1 AAAA
2 BBBB
3 CCCC
4 DDDD
YYYY
1 AAAA
2 BBBB
3 CCCC
4 DDDD

Desired output:

XXXX AAAA
XXXX BBBB
XXXX CCCC
XXXX DDDD
YYYY AAAA
YYYY BBBB
YYYY CCCC
YYYY DDDD

Any help would be appreciated.

Does it have to be sed?

awk 'NF==1{x=$1}NF==2{$1=x;print}' file

no it doesn't need to be sed. I'm not getting any output.

What operating system are you using? Do you have more fields in your file?

Yes it's working, there were a 2nd set of fields in the file! Thank you so much. Cheers!

With sed:
sed -n '/^[^1-4]/h;/^[1-4]/{G;s/^[1-4]//;s/\(.*\)\n\(.*\)/\2\1/;p}' <file
--
Bye