原文：https://cran.r-project.org/web/packages/ggtext/vignettes/plotting_text.html

ggtext包定義了兩個新的geoms, geom_richtext()和geom_textbox()翅睛，用于為圖形進(jìn)行文本標(biāo)記匿又， 分別繪制簡單的文本標(biāo)記（沒有自動換行）和文本框（帶自動換行）

使用geom_richtext()理肺，能將markdown形式的文本標(biāo)置于圖形中⊥龊牵可以看做是以前常用的geom_label()或geom_text()的代替品。

例子1——簡單文本標(biāo)記

• 使用r2的值添加圖形注釋助琐，用iris數(shù)據(jù)為例憎账，用傳統(tǒng)的geom_text()標(biāo)記如下：

library(ggplot2)
library(dplyr)
library(glue)

iris_cor <- iris %>% 
  group_by(Species) %>%
  summarize(r_square = cor(Sepal.Length, Sepal.Width)^2) %>%
  mutate(
    # location of each text label in data coordinates
    Sepal.Length = 8, Sepal.Width = 4.5,
    # text label containing r^2 value 
    label = glue("r^2 = {round(r_square, 2)}")
  )

iris_cor
#> # A tibble: 3 x 5
#>   Species    r_square Sepal.Length Sepal.Width label     
#>   <fct>         <dbl>        <dbl>       <dbl> <glue>    
#> 1 setosa        0.551            8         4.5 r^2 = 0.55
#> 2 versicolor    0.277            8         4.5 r^2 = 0.28
#> 3 virginica     0.209            8         4.5 r^2 = 0.21

iris_facets <- ggplot(iris, aes(Sepal.Length, Sepal.Width)) +
  geom_point() + 
  geom_smooth(method = "lm", formula = y ~ x) +
  facet_wrap(~Species) +
  theme_bw()

iris_facets + 
  geom_text(
    data = iris_cor,
    aes(label = label),
    hjust = 1, vjust = 1

image.png

代碼可以work趴捅，但是結(jié)果不讓人滿意垫毙。1）r是數(shù)學(xué)變量，應(yīng)該斜體拱绑。2）2應(yīng)該是上標(biāo)不是^2综芥。用geom_richtext()可以輕松創(chuàng)建markdown標(biāo)記。

library(ggtext)

iris_cor_md <- iris_cor %>% 
  mutate(
    # markdown version of text label
    label = glue("*r*<sup>2</sup> = {round(r_square, 2)}")
  )

iris_cor_md
#> # A tibble: 3 x 5
#>   Species    r_square Sepal.Length Sepal.Width label                 
#>   <fct>         <dbl>        <dbl>       <dbl> <glue>                
#> 1 setosa        0.551            8         4.5 *r*<sup>2</sup> = 0.55
#> 2 versicolor    0.277            8         4.5 *r*<sup>2</sup> = 0.28
#> 3 virginica     0.209            8         4.5 *r*<sup>2</sup> = 0.21

iris_facets + 
  geom_richtext(
    data = iris_cor_md,
    aes(label = label),
    hjust = 1, vjust = 1
  )

image.png

默認(rèn)情況下猎拨，geom_richtext() 要給文本加一個框膀藐，可以通過設(shè)置填充色和外框線的顏色讓它不可見 (fill = NA, label.colour = NA)屠阻。

iris_facets + 
  geom_richtext(
    data = iris_cor_md,
    aes(label = label),
    hjust = 1, vjust = 1,
    # remove label background and outline
    fill = NA, label.color = NA,
    # remove label padding, since we have removed the label outline
    label.padding = grid::unit(rep(0, 4), "pt") 
  )

image.png

如同ggplot2一樣，可以各自選擇偏愛的標(biāo)記線额各、填充和文章的顏色国觉。

iris_facets + 
  aes(colour = Species) +
  geom_richtext(
    data = iris_cor_md,
    aes(
      label = label,
      fill = after_scale(alpha(colour, .2))
    ),
    text.colour = "black",
    hjust = 1, vjust = 1
  ) +
  theme(legend.position = "none")

image.png

還可以旋轉(zhuǎn)文字標(biāo)記（雖然不建議這么做）。

iris_facets + 
  aes(colour = Species) +
  geom_richtext(
    data = iris_cor_md,
    aes(
      x = 7.5,
      label = label,
      fill = after_scale(alpha(colour, .2))
    ),
    text.colour = "black",
    hjust = 1, vjust = 1,
    angle = 30
  ) +
  theme(legend.position = "none")

image.png

文本框

用geom_textbox()為圖形添加markdown形式的文本框（帶自動換行）虾啦÷榫鳎可以指定文本框的寬度，可以是絕對寬度（如"cm","pt", "in")傲醉，也可以是相對寬度(如"npc")蝇闭。

df <- data.frame(
  x = 0.1,
  y = 0.8,
  label = "*Lorem ipsum dolor sit amet,* consectetur adipiscing
elit. Quisque tincidunt eget arcu in pulvinar. Morbi varius leo
vel consectetur luctus. **Morbi facilisis justo non fringilla.**
Vivamus sagittis sem felis, vel lobortis risus mattis eget. Nam
quis imperdiet felis, in convallis elit."
)

p <- ggplot() +
  geom_textbox(
    data = df,
    aes(x, y, label = label),
    width = grid::unit(0.73, "npc"), # 73% of plot panel width
    hjust = 0, vjust = 1
  ) +
  xlim(0, 1) + ylim(0, 1)

p

image.png

如果改變了圖形的寬度，文本框會隨著改變硬毕，文本自動適應(yīng)呻引。

image.png

用hjust和vjust對齊x和y軸定義的參考點(diǎn)，它不會影響文本框中的文本吐咳。文本框的文本對齊逻悠，可以用halign和valign。例如用halign=0.5進(jìn)行中心文本對齊挪丢。

ggplot() +
  geom_textbox(
    data = df,
    aes(x, y, label = label),
    width = grid::unit(0.73, "npc"), # 73% of plot panel width
    hjust = 0, vjust = 1,
    halign = 0.5 # centered text
  ) +
  xlim(0, 1) + ylim(0, 1)

image.png

文本框雖然不能任意角度旋轉(zhuǎn)蹂风，但是可以有四個選擇。

df <- data.frame(
  x = 0.5,
  y = 0.5,
  label = "The quick brown fox jumps over the lazy dog.",
  orientation = c("upright", "left-rotated", "inverted", "right-rotated")
)

ggplot() +
  geom_textbox(
    data = df,
    aes(x, y, label = label, orientation = orientation),
    width = grid::unit(1.5, "in"),
    height = grid::unit(1.5, "in"),
    box.margin = grid::unit(rep(0.25, 4), "in"),
    hjust = 0, vjust = 1
  ) +
  xlim(0, 1) + ylim(0, 1) +
  scale_discrete_identity(aesthetics = "orientation")

image.png