格图标题中的斜体

Question

我已阅读有关如何在图表标题中创建斜体字的帖子，但它似乎对我不起作用。

#create a list of species
sp <- c("Etelis coruscans","Etelis carbunculus","Pristipomoides sieboldii","Pristipomoides filamentosus","Pristipomoides zonatus","Epinephelus quernus","Aphareus rutilans")

#plot hisotgrams for each spp in 1cm bins
for (i in sp){
    BIN_WIDTH <- 1 #desired bin width
    print(histogram(~ Length..cm. | Method, #create and print the histogram and save to variable "graph"
    data = hist.data[hist.data$Scientific_name == i,], 
    nint = (max(hist.data$Length..cm.) - min(hist.data$Length..cm.)+1)/BIN_WIDTH,
    layout = c(1,2),
    main = paste("Length-Frequency of", italic(i), "by Gear"), sep = " ",
    xlab = "Length (cm)"))

    #save histogram to PNG file
    quartz.save(paste("*Length-Frequency of", i, "by method.png", sep = " "), type = "png")
    dev.off() #close the graphics diver
}

我收到一条错误消息：

Error in print(histogram(~Length..cm. | Method, data = hist.data[hist.data$Scientific_name ==  : 
  error in evaluating the argument 'x' in selecting a method for function 'print': Error in paste(italic("Length-Frequency of", i, "by Gear")) : 
  could not find function "italic"

谁能指出我做错了什么？

Answer 1

您传递给main 的参数需要进行一些更改。

• 要使用 R 的 plotmath 特殊功能（即 italic() 之类的东西），它应该是一个表达式对象而不是字符串。这意味着做这样的事情：

  main = expression(paste("Length-Freq of", italic("E. coruscans"), "by Gear"))
  

  而不是这个：

  main = paste("Length-Freq of", italic("E. coruscans"), "by Gear")
  

• 另外，你想要斜体i的值而不是它的名称，但是如果你只输入italic(i)，lattice会渲染@987654328 @ 的名称为每个物种的小斜体“i”。使用bquote() 或substitute() 替换i 的值，如下所示：

  i <- "E. coruscans"
  xyplot(1:10~1:10,
      main = substitute(expr = expression(paste("Species name: ", italic(i))), 
                        env = list(i=i)))