输入S4对象

Question

一个人如何dput()一个S4对象？我试过了

require(sp)
require(splancs)
plot(0, 0, xlim = c(-100, 100), ylim = c(-100, 100))
poly.d <- getpoly() #draw a pretty polygon - PRETTY!
poly.d <- rbind(poly.d, poly.d[1,]) # close the polygon because of Polygons() and its kin
poly.d <- SpatialPolygons(list(Polygons(list(Polygon(poly.d)), ID = 1)))
poly.d
dput(poly.d)

请注意，如果我对S4对象执行dput()操作，则无法再次重新构造它。你的想法是什么？

Answer 1

按照目前的情况，您无法对此对象执行dput操作。dput的代码包含以下循环：

if (isS4(x)) {
    cat("new(\"", class(x), "\"\n", file = file, sep = "")
    for (n in slotNames(x)) {
        cat("    ,", n, "= ", file = file)
        dput(slot(x, n), file = file, control = control)
    }
    cat(")\n", file = file)
    invisible()
}

这以递归方式处理S4对象，但它依赖于假设S3对象将不包含S4对象，在您的示例中不包含：

> isS4(slot(poly.d,'polygons'))
[1] FALSE
> isS4(slot(poly.d,'polygons')[[1]])
[1] TRUE

编辑：这里是一个绕过dput限制的解决方案。它适用于您提供的示例，但我认为它不会在一般情况下工作(例如，它不处理属性)。

dput2 <- function (x,
                   file = "",
                   control = c("keepNA", "keepInteger", "showAttributes")){
    if (is.character(file))
        if (nzchar(file)) {
            file <- file(file, "wt")
            on.exit(close(file))
        }
        else file <- stdout()
    opts <- .deparseOpts(control)
    if (isS4(x)) {
        cat("new(\"", class(x), "\"\n", file = file, sep = "")
        for (n in slotNames(x)) {
            cat("    ,", n, "= ", file = file)
            dput2(slot(x, n), file = file, control = control)
        }
        cat(")\n", file = file)
        invisible()
    } else if(length(grep('@',capture.output(str(x)))) > 0){
      if(is.list(x)){
        cat("list(\n", file = file, sep = "")
        for (i in 1:length(x)) {
          if(!is.null(names(x))){
            n <- names(x)[i]
            if(n != ''){
              cat("    ,", n, "= ", file = file)
            }
          }
          dput2(x[[i]], file = file, control = control)
        }
        cat(")\n", file = file)
        invisible()
      } else {
        stop('S4 objects are only handled if they are contained within an S4 object or a list object')
      }
    }
    else .Internal(dput(x, file, opts))
}

这就是它的实际作用：

> dput2(poly.d,file=(tempFile <- tempfile()))
> poly.d2 <- dget(tempFile)
> all.equal(poly.d,poly.d2)
[1] TRUE