我有一个如下所示的数据集:
rownum<-c(1,2,3,4,5,6,7,8,9,10)
name<-c("jeff","jeff","mary","jeff","jeff","jeff","mary","mary","mary","mary")
text<-c("a","b","c","d","e","f","g","h","i","j")
a<-data.table(rownum,name,text)
我想添加一个新的文本列,从前一列中添加rownum和name.新列的向量将是:
rolltext<-c("a","ab","c","abd","abde","abdef","cg","cgh","cghi","cghij"
在这方面我无所适从.对于数字我只会使用cumsum函数,但对于文本我认为我需要for循环或使用其中一个apply函数？