格子图的标题中的斜体

Question

我已经阅读了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
}

我收到错误说：

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"

有人可以指出我做错了吗？

Answer 1

您传递给main的论点需要进行一些更改。

• 要使用R的plotmath特殊内容（例如italic()之类的内容），它应该是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：

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

• 此外，您希望将i的值而不是名称设为斜体，但如果只输入{{1} }，格子会将italic(i)的名称呈现为每个物种的一个小斜体“ i ”。使用i或bquote()代替substitute()的值，如下所示：

  i