Question

编辑：添加完整代码

我为“情节”做了一个S4方法似乎正在工作，除了它向控制台输出一些迷路NULL，我无法弄清楚它来自哪里。这是顶级代码：

print(plot(x = flux, y = 1, fastplot = TRUE, quietly = TRUE))

上课：

flux <- setClass(
  # Set the class name
  "flux",
  slots = c(
     raw.data = "list",
     source.files = "character",
     data = "matrix",
     time = "POSIXct",
     datatype = "character",
     metadata = "data.frame"
  )
)

方法：

setMethod("plot",
      signature(x = "flux"),
      function (x, y, ...) {
        CheckFluxObject(x)
        params <- LoadDefaults(flux = x)
        # Interpret 'plot' arguments
        par.restore <- par(no.readonly = TRUE)
        on.exit(expr = par(par.restore), add = TRUE)
        arguments <- list(...)
        if (!("fastplot" %in% names(arguments))) {
          fastplot <- FALSE
        } else {
          fastplot <- arguments$fastplot
          arguments$fastplot <- NULL
        }
        if (!("quietly" %in% names(arguments))) {
          quietly <- FALSE
        } else {
          quietly <- arguments$quietly
          arguments$quietly <- NULL
        }
        par(ask=!(fastplot))
        if (!("ylab" %in% arguments)) {
          ylab <- params["units"]
        } else {
          ylab <- arguments$ylab
          arguments$ylab <- NULL
        }
        # Pull relevant 'flux' class object data
        data <- slot(x, "data")
        if (missing("y")) {
          y <- 1:ncol(data)
        } else {
          stopifnot(
            is.integer(y),
            all(y %in% 1:ncol(data))
          )
        }
        # Bulk function execution
        if (quietly == FALSE) {
          message("Plotting data traces:")
        }
        plot.obj <- plot.new()
        print("NULL is in the 'for' loop...")
        for (i in y){
          main <- colnames(data)[i]
          plot.obj <- plot(slot(x, "time"), data[, i], main = main,
                           xlab = "Time", ylab = ylab, unlist(arguments))
          print(plot.obj)
        }
        print("but is it also here??")
        # Clean-up and exit
        if (quietly == FALSE) {
          message("Done plotting.")
        }
        if (length(y) == 1) {
          invisible(plot.obj)
        }
        print("or here??")
        invisible(NULL)
      }
)

输出是：

[1] "NULL is in the 'for' loop..."
NULL
[1] "but is it also here??"
[1] "or here??"
NULL

如果我在print("what about here??")之后再投掷invisible(NULL)，然后就是这样：

[1] "NULL is in the 'for' loop..."
NULL
[1] "but is it also here??"
[1] "or here??"
[1] "what about here??"
[1] "what about here??"

我有没有预料到函数返回或打印命令的某些行为？ CheckFluxObject函数只是检查以确保所有插槽都已填满。

Answer 1

如果有的话，我会把这个留在这里直到更好的答案出现：

显然，绘图对象的print方法会返回NULL，如果您尝试在函数中生成绘图，那么最好的方法就是使用{{ 1}}或invisible(plot.object)，不是invisible(plot(x, y, ...))。

我还不确定第二个NULL来自哪里......

编辑：找到第二个！就像方法本身中的print一样，顶级代码中的print(plot.obj)会抛出print。删除所有NULL命令会杀死所有鬼魂。

杀死ghost NULL控制台输出？

1 个答案: