r - 自定义格函数(组参数)中的范围

Question

请考虑这个函数:

tf <- function(formula = NULL, data = NULL, groups = NULL) {

    grv <- eval(substitute(groups), data, environment(formula)) # the values
    grn <- as.character(match.call()$groups) # the name
    gr <- match.call()$groups # unquoted name

    p <- xyplot(formula, data, # draws the data but not in groups
# Try these options:
#   p <- xyplot(formula, data, groups, # can't find 'cat2' 
#   p <- xyplot(formula, data, groups = data[,grn], # can't fine grn
#   p <- xyplot(formula, data, groups = grv, # can't find grv
        panel = function(x, y) {
            panel.stripplot(x, y, jitter.data = TRUE, pch = 20)
            }
            )
    p
    }

你可以运行:

tf(formula = mpg~vs, groups = am, data = mtcars)

我在将 groups 参数传递给 xyplot 时做错了什么 - 为什么找不到它？我不知道它是如何需要 group 信息的。谢谢。

更新:

@agstudy 的回答很有帮助，但是如果我像原来的例子一样添加面板功能，仍然无法识别组(没有分组，但也没有发生错误):

tf <- function(formula = NULL, data = NULL, groups = NULL) {
    ll <- as.list(match.call(expand.dots = FALSE)[-1])
    p <- xyplot(as.formula(ll$formula), 
              data = eval(ll$data), 
              groups = eval(ll$groups),
                panel = function(x, y) {
                panel.stripplot(x, y, jitter.data = TRUE, pch = 20)
                }
                )
    p
    }

有些东西仍然缺失......谢谢。

Answer 1

您可以在此处使用 eval，因为 match.call 会返回符号。

tf <- function(formula = NULL, data = NULL, groups = NULL) {
  ll <- as.list(match.call(expand.dots = FALSE)[-1])
  p <- xyplot(as.formula(ll$formula), 
              data = eval(ll$data), 
              groups = eval(ll$groups),
              panel = function(x, y,...) { ## here ... contains groups and subscripts
                ## here you can transform x or y before giving them to the jitter
                panel.stripplot(x, y, jitter.data = TRUE, pch = 20,...)
              }
  )
  p
}