R data.table:j中的匿名函数

我试图让一个匿名函数在

data.table

的

j

参数中返回多列。下面是一个例子：

## sample data
tmpdt <- data.table(a = c(rep("a", 5), rep("b", 5)),
                    b = c(rep("f", 3), rep("r", 7)),
                    c = 1:10,
                    d = 21:30)
tmpdt[c %in% c(2,4), c := NA]

## this works fine
tmpdt[ , list(testout =
                (function(x) {
                    model <- lm(c ~ d, x)
                    residuals(model)
                })(.SD)),
      by = a]

## but I want to return a data.frame from the
## anonymous function

tmpdt[ , list(testout =
                (function(x) {
                    model <- lm(c ~ d, x)
                    tmpresid <- residuals(model)
                    tmpvalue <- x$b[as.numeric(names(tmpresid))]
                    data.frame(tmpvalue, tmpresid)
                })(.SD)),
      by = a]

##样本数据
tmpdt在我做了这件事之后就意识到了这个问题。无需列出：

tmpdt[,(function(x) {
                    model <- lm(c~d,x)
                    tmpresid <- residuals(model)
                    tmpvalue <- x$b[as.numeric(names(tmpresid))]
                    data.frame(tmpvalue,tmpresid)
                })(.SD)),
      by=a]

tmpdt[，（函数（x）{
model您不需要匿名函数-您可以在
j
中的
{}
（匿名体）中包装任意表达式

tmpdt[, {
          model <- lm(c ~ d, .SD)
          tmpresid <- residuals(model)
          tmpvalue <- b[as.numeric(names(tmpresid))]
          list(tmpvalue, tmpresid) # every element of the list becomes a column in result
        }
      , by = a]

tmpdt[,{
模特更优雅，谢谢。