R将向量转换为数字参考

我需要把向量转换成数字字符串。我尝试了中的解决方案，但收到错误消息

例如，使用此数据集：

v1 <- rep(c('a','b'),3)
v2 <- rep(c('c','d','e'),2)
vdf <- data.frame(v1, v2)

sapply(vdf, class)
      v1       v2 
"factor" "factor" 

sapply(vdf, mode) #I'm not sure why the mode shows as numeric as the value is a charecter
       v1        v2 
"numeric" "numeric" 

---

v1多亏了Sotos的评论，我才能够轻松解决这个问题。根据他的评论，对我有效的解决方案是

vdf[]
vdf[]有效。谢谢Sotos
vdf
v1c <- rep(c(1,2),3)
v2c <- rep(c(1,2,3),2)
vdfc <- data.frame(v1c, v2c)

sapply(vdfc, class)
      v1c       v2c 
"numeric" "numeric" 
     sapply(vdfc, mode)
      v1c       v2c 
"numeric" "numeric" 

df$iv1 = as.integer(df$v1) 
df$iv1 = as.integer(as.factor(df$v1))

Error in `$<-.data.frame`(`*tmp*`, "iv1", value = integer(0)) : replacement has 0 rows, data has 10