代码如下：
write.csv(Percentiles,"C:/R/Quantiles of Marriage Pregnancy Intervals.csv",row.names=FALSE)
require(RColorBrewer)
require(ggthemes)
tab<-read.csv("C:/R/Quantiles of Marriage Pregnancy Intervals.csv",header=TRUE)
names(tab)[3]<-"value"
tab<-reshape2::dcast(tab,Year+Class~P)
tab<-tab[,c("Year","Class",as.character(0:9),">=10")]
报错：Error in `[.data.frame`(tab, , c("Year", "Class", as.character(0:9), ">=10")) :
  undefined columns selected。想请教下原因及其解决方法