DATA Q; INPUT Trt $; DO Replication = 1 TO 4; INPUT Y @@; OUTPUT; END; CARDS; Trt1 23 27 19 21 Trt2 18 17 20 15 Trt3 29 31 32 34

proc print; RUN;

If I run this in SAS, I obtain the following output:

Obs	Trt	Replication	Y
1	Trt1	1	.
2	Trt1	2	18
3	Trt1	3	17
4	Trt1	4	20
5	15	1	.
6	15	2	29
7	15	3	31
8	15	4	32

Could you give me a break down of how this output is obtained?