R中图例中的斜体字和非斜体字？

Question

我需要绘制发现的紫罗兰色标本随时间变化的曲线。在图例中，我想显示两个观察到的物种以及它们的总和。为了撰写科学正确的文章，我还需要在“中提琴规格总和”中为“中提琴”添加斜体。

我实际上希望与他的右上角传说中的theforestecologist相同，但是我无法用单词来重现他的例子。因此，我使用text.font()轻松实现了这一点，但是整行都是斜体的。我在main()中使用的代码缩写没有帮助。 是否可以在图例中仅用斜体写一行？

vr <- sample(1:100, 10, replace = TRUE)
vo <- sample(1:100, 10, replace = TRUE)
date <- Sys.Date() + sort(sample(1:10, 10))
vs <- vr + vo
df <- data.frame(vr, vo, date, vs)

plot(
  vs ~ date,
  data = df,
  type = "o",
  ylim = c(0, max(df$vs)),
  col = "black",
  pch = 13,
  cex = 1.2,
  lwd = 2,
  main = expression(paste(italic('Viola'), " spec. [ind]")),
  ylab = "Amount"
)
lines(
  vr ~ date,
  data = df,
  type = "o",
  col = "RoyalBlue2",
  pch = 1,
  cex = 1.2
)
lines(
  vo ~ date,
  data = df,
  type = "o",
  col = "springgreen3",
  pch = 4,
  cex = 1.2
)
legend(
  "topright",
  inset = c(0.01 , 0.02),
  c("Sum of Viola spec.", "Viola odorata", "Viola reichenbachiana"),
  xpd = TRUE,
  pch = c(13, 1, 4),
  pt.cex = 1.2,
  col = c(1, "RoyalBlue2", "springgreen3"),
  cex = .9,
  y.intersp = .9,
  bty = "l",
  bg = rgb(244, 248, 249, max = 255),
  text.font = c(1, 3, 3)
)

Answer 1

为什么不像标题那样使用expression()和italic()？

legend(
  "topright", 
  inset=c(0.01 ,0.02), 
  c(expression(paste("Sum of ", italic('Viola'), " spec.")), 
    expression(italic("Viola odorata")), 
    expression(italic("Viola reichenbachiana"))
    ), 
  xpd = TRUE,
  pch = c(13, 1, 4), pt.cex=1.2, 
  col = c(1,"RoyalBlue2", "springgreen3"), 
  cex = .9, y.intersp=.9, bty = "l", 
  bg = rgb(244, 248, 249, max = 255), 
  text.font = c(1,3,3)
)