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c("1","2","3","4")变成c(1,2,3,4)
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两种形式来回切换，不需要手动修改，
{r eval=F} c("1", "2", "3", "4") c("1","2","3","4")
c("1","2","3","4")变成c(1,2,3,4)
两种形式来回切换，不需要手动修改，
{r eval=F} c("1", "2", "3", "4") c("1","2","3","4")