我想计算自变量x1（连续变量）与亚组x2的相加交互作用，调整因素为X3，X4。程序参考文献《Logistic回归模型中连续变量交互作用的分析》。具体如下：
additive1 <- read.csv('C:/xxxxxxxxxxxxxxxxxxxxx)
dat.add <- glm(Y ~  X1*as.factor(x2) + X3 + X4,
               family = binomial, data=additive1)
summary(dat.add)

s2 <- function(datsam,indices){
  +d<-datsam[indices,]
  +fitlr <- glm(Y ~  X1*as.factor(x2) + X3 + X4,
             family = binomial, data=d)
  +s <- (exp(fitlr$coef[2]+fitlr$coef[3]+fitlr$coef[6])-1/(exp(fitlr$coef[2])-1+exp(fitlr$coef[3])-1))}

outs2 <- boot(data=dat.add, statistic = S2, R=1000)
print(outs2)
plot(outs2)
boot.ci(outs2,conf=0.95,type="perc")


可是最后提示“Error in boot(data = dat.add, statistic = S2, R = 1000) :
  object 'S2' not found”
请问如何修改呢？