wtpmean=aggregate(dat$A20,by=list(dat$sub),mean)
colnames(wtpmean)=c("sub","mean")
wtpsd=aggregate(dat$A20,by=list(dat$sub),sd)
colnames(wtpsd)=c("sub","sd")
(subset(dat$A20,dat$sub==1)-wtpmean$mean[1])/wtpsd$sd[1]
##結果
>[1] -0.9647826  0.1146944  0.1146944 -0.1551748  0.6544330 -0.8028611  2.0037793
[8] -0.9647826
成功出現sub=1的8次觀察值zscore##
#想要把這個寫成迴圈，受試者共有117位，每位有8個觀察值
> zscore=0
> for(i in 1:936){
+ zscore[i]=(subset(dat$A20,dat$sub==i)-wtpmean$mean[i])/wtpsd$sd[i]}
##
Error in zscore[i] = (subset(dat$A20, dat$sub == i) - wtpmean$mean[i])/wtpsd$sd[i] :
  replacement has length zero
In addition: There were 50 or more warnings (use warnings() to see the first 50)##