使用R中的循环在现有数据R中创建列

Question

我试图根据四个变量在现有的数据框架中创建四列。由于它们都使用相同的逻辑，所以我决定执行一个循环，而不是复制和粘贴代码4次。然而，我在循环上遇到了麻烦。下面是我为循环编写的代码。

names<-c("a 1", "b 1", "c 1", "d 1")

for (k in names){ 

Large_Data$column_k <- ifelse(Large_Data$`k`== "I-2", 2,
                                +    ifelse(Large_Data$`k`== "I-3", 3,
                                +    ifelse(Large_Data$`k`== "I-4", 4,
                                +    ifelse(Large_Data$`k`== "I-5", 5,
                                +    ifelse(Large_Data$`k`== "I-6", 6,
                                +    ifelse(Large_Data$`k`== "I-7", 7,
                                +    ifelse(Large_Data$`k`== "S-1", 8,
                                +    ifelse(Large_Data$`k`== "S-2", 9,
                                +    ifelse(Large_Data$`k`== "S-3", 10,
                                +    ifelse(Large_Data$`k`== "S-4", 11,
                                +    ifelse(Large_Data$`k`== "P-1", 12,
                                +    ifelse(Large_Data$`k`== "P-2", 13,
                                +    ifelse(Large_Data$`k`== "P-3", 14,
                                +    ifelse(Large_Data$`k`== "D-1", 15,
                                +    ifelse(Large_Data$`k`== "D-2", 16,
                                99)))))))))))))))


}

我希望在这个问题上有任何帮助。谢谢。

Answer 1

如何构建查找表

library(data.table)
letter=c('I','S','P','D')
start=c(2,1,1,1)
end=c(7,4,3,2)
label=2:16 # correspond to the I-2, I-3,..S1,S2,... values in that order
code.table=data.table(letter,start,end)
code.vector=unlist(apply(code.table,1,function(x) paste(x[1],x[2]:x[3],sep='-')))
lookup.table=data.table(code=code.vector,label=label)

一旦建立了查找表，您就可以创建一个函数，该函数合并您的表并获取标签，并将该函数应用于所有列名。

getlabel=function(x)    merge(Large_Data,lookup.table,by.x=x,by.y="code",all.x=TRUE,sort=F)$label
lapply(names,function(x) Large_Data[,paste(x,"label",sep="_"):=getlabel(x)])

Answer 2

似乎您的问题可以更容易地通过某种查找表和合并两个dataframes来解决，而不是所有的ifelse语句。

示例：

lookup.table = structure(list(cyl = c(4L, 6L, 8L), new = structure(c(2L, 3L, 
1L), .Label = c("eight", "four", "six"), class = "factor")), .Names = c("cyl", 
"new"), class = "data.frame", row.names = c(NA, -3L))

merge(mtcars,lookup.table,by="cyl")