如果没有错误的R函数没有返回值，如何返回值

Question

我的目标是将pyramid package生成的图分配给列表。稍后，我将把该图和列表中的其他图插入到文档中。但是pyramid function似乎没有返回值。如何将棱锥图指定给对象？

install.packages("pyramid") # functions to draw a population pyramid
library(pyramid)
# create a mock data frame to comparing this plot to a counterpart from plotrix
df <- data.frame(level1 = c(9,9,4,3,34,28), levelsame = c(9,9,4,3,34,28),
 title = c("Dir", "Exec. Dir", "Mgr", "Sr. Mgr", "Mgt Princ", "EVP+"))
        # assign the plot (hopefully) to an object
empty <- pyramid(df, Laxis = seq(1,35,5), AxisFM = "g", Csize = 0.8, Cgap = .5, Llab = "",
                                 Rlab = "", Clab = "Title", GL = F, Lcol = "blue", Rcol = "blue",
                                 Ldens = -1, main = "Distribution of Levels")
> empty
NULL

同样，如果我将金字塔调用分配给我的列表，则不会发生任何事情。pyramid返回的列表没有值。

plotlist2[["pyramid"]] <-  pyramid(df, Laxis = seq(1,35,5), AxisFM = "g", Csize = 0.8, Cgap = .5, Llab = "",
                                  Rlab = "", Clab = "Title", GL = F, Lcol = "blue", Rcol = "blue",
                                  Ldens = -1, main = "Distribution of Levels")
> plotlist2[1]
[[1]]
NULL

我担心我在一些明显的错误理解上犯了错误，所以我欢迎被纠正。非常感谢。

Answer 1

您可以使用recordPlot()函数将当前绘图保存到变量中。

在你的情况下，你可以做：

#print the plot
pyramid(df, Laxis = seq(1,35,5), AxisFM = "g", Csize = 0.8, Cgap = .5, Llab = "",
        Rlab = "", Clab = "Title", GL = F, Lcol = "blue", Rcol = "blue",
        Ldens = -1, main = "Distribution of Levels")
#save the current printed plot
pyrPlot<-recordPlot()
#plot it again
pyrPlot

您可能必须使用dev.control(displaylist ="enable")启用显示列表才能工作，这取决于您使用的图形设备