Shell Programming and Scripting

Hello all, I need help with excluding the rows in which the data in the first column occur only once. For example;

DATA-1 8374 XX YY
DATA-1 9838 AB DD
DATA-1 8377 CC XY
DATA-2 8737 AB DD
DATA-3 7626 DC DD
DATA-3 8722 AB RE
DATA-4 8982 CD XY
DATA-5 7762 AC RT
DATA-5 8722 AD TD

So I want to get of rows number 4 (DATA-2 ......) and row number 7 (DATA-4 .....) as in these the data in the first column occurs only once.

Please help.

If the first column has a fixed width:

uniq -w 6 -u datafile.txt

if not:

cut -d" " -f1 datafile.txt | uniq -u | while read a ; do grep -e "^${a}" datafile.txt ; done

Thanks for your prompt solution to my problem. I also want to thank you for your answer yesterday for my problem. I highly appreciate it. God Bless.