levels<-c("a","b","c","d")
for (i in 1:14) {
apf1<-t.test(data[var2==levels[i],]$var1.x,data[var2==levels[i],]$var1.y,mu=0, alt="two.sided", paired=T)

apf1
}
请问大家这个循环错在哪里啊，为什么不显示结果