mean （of c1-c4)正确
mean(c1-c4)错误, mean(c1-c4)表示c1列的值减去c4列的值，就成了一个数，然后求均数

egen mean=rowmean(c1-c4)

楼主正确

data test;
input C1 C2 C3 C4;
datalines;
4 3 21 45
54 2 2 54
545 3 3 45
4 2 53 21
55 3 3 545
5 5 4 54
; run;
data result;
   set test;
   row_mean = mean(of c1-c4);
run;

mean的时候不能用c1-c4,如果是我要合并c1,c2,c3,c4，比如 Data analysis; merger c1-c4,这个可以吗