r - 即使对于 ggplot2 中的重叠区域，相同/修复 alpha

Question

我想先绘制一堆区域，然后用相同的单个 alpha 值显示生成的整体区域。所以不要这样:

library(tidyverse)

dat <- tribble(
  ~xmin, ~xmax, ~ymin, ~ymax,
     10,    30,    10,    30,
     20,    40,    20,    40,
     15,    35,    15,    25,
     10,    15,    35,    40
)

ggplot() +
  geom_rect(data = dat,
            aes(
              xmin = xmin,
              xmax = xmax,
              ymin = ymin,
              ymax = ymax
            ),
            alpha = 0.5)

我希望将其作为我的结果:

^{由 reprex package 于 2022-07-26 创建(v2.0.1)}

我觉得我的问题的答案可能与 this thread 中的答案相似但我并不完全理解它，因此不确定。另请注意，我使用 geom_rect() 作为代表，但最终我希望它适用于 ggforce::geom_circle() .

编辑 1

Quinten's first answer ，它指向 scale_alpha(range = ..., limits = ...)，不幸的是没有回答我的问题，因为它显然只能导致不透明的区域。

编辑 2

Quinten's updated answer是我可以接受上述代表的一种解决方法。但是，正如我上面提到的，我希望它适用于 ggforce::geom_circle() .不幸的是，我想我现在必须更具体并创建另一个代表。 (对不起)

library(ggforce)
#> Lade nötiges Paket: ggplot2

dat <- data.frame(
  x = c(1, 1.3, 1.6),
  y = c(1, 1, 1),
  circle = c("yes", "yes", "no")
)

ggplot() +
  coord_equal() +
  theme_classic() +
  geom_circle(
    data = subset(dat, circle == "yes"),
    aes(x0 = x, y0 = y, r = 0.5, alpha = circle),
    fill = "grey",
    color = NA,
    show.legend = TRUE
  ) +
  geom_point(
    data = dat,
    aes(x, y, color = circle)
  ) +
  scale_color_manual(
    values = c("yes" = "blue", "no" = "red")
  ) +
  scale_alpha_manual(
    values = c("yes" = 0.25, "no" = 0)
  )

^{由 reprex package 于 2022-08-17 创建(v2.0.1)}

Answer 1

ggblend

不久前我还看到了 ggblend，但不确定它是否能解决您的问题，幸运的是它可以解决!你可以做两件事:

1. 您可以像这样将 Rstudio 中的 Graphics 更改为“Cairo”:

代码:

#remotes::install_github("mjskay/ggblend")
library(ggblend)
library(ggforce)

# reprex 1 ----------------------------------------------------------------
library(tidyverse)

dat <- tribble(
  ~xmin, ~xmax, ~ymin, ~ymax,
  10,    30,    10,    30,
  20,    40,    20,    40,
  15,    35,    15,    25,
  10,    15,    35,    40
)

p1 <- ggplot() +
  geom_rect(data = dat,
            aes(
              xmin = xmin,
              xmax = xmax,
              ymin = ymin,
              ymax = ymax
            ),
            alpha = 0.3) %>% blend("source")

p1

# reprex 2 ----------------------------------------------------------------
dat <- data.frame(
  x = c(1, 1.3, 1.6),
  y = c(1, 1, 1),
  circle = c("yes", "yes", "no")
)

p2 <- ggplot() +
  coord_equal() +
  theme_classic() +
  geom_circle(
    data = subset(dat, circle == "yes"),
    aes(x0 = x, y0 = y, r = 0.5, alpha = circle),
    fill = "grey",
    color = NA,
    show.legend = TRUE
  ) %>% blend("source") +
  geom_point(
    data = dat,
    aes(x, y, color = circle)
  ) +
  scale_color_manual(
    values = c("yes" = "blue", "no" = "red")
  ) +
  scale_alpha_manual(
    values = c("yes" = 0.25, "no" = 0)
  )

p2
#ggsave(plot = p2, "p2.pdf", device = cairo_pdf)

1. 您可以使用 type = "cairo" 将对象保存为 png，如下所示:

library(ggblend)
library(ggforce)

# reprex 1 ----------------------------------------------------------------
library(tidyverse)

dat <- tribble(
  ~xmin, ~xmax, ~ymin, ~ymax,
  10,    30,    10,    30,
  20,    40,    20,    40,
  15,    35,    15,    25,
  10,    15,    35,    40
)

p1 <- ggplot() +
  geom_rect(data = dat,
            aes(
              xmin = xmin,
              xmax = xmax,
              ymin = ymin,
              ymax = ymax
            ),
            alpha = 0.3) %>% blend("source")
#> Warning: Your graphics device, "quartz_off_screen", reports that blend = "source" is not supported.
#>  - If the blending output IS NOT as expected (e.g. geoms are not being
#>    drawn), then you must switch to a graphics device that supports
#>    blending, like png(type = "cairo"), svg(), or cairo_pdf().
#>  - If the blending output IS as expected despite this warning, this is
#>    likely a bug *in the graphics device*. Unfortunately, several
#>    graphics do not correctly report their capabilities. You may wish to
#>    a report a bug to the authors of the graphics device. In the mean
#>    time, you can disable this warning via options(ggblend.check_blend =
#>    FALSE).
#>  - For more information, see the Supported Devices section of
#>    help('blend').

png(filename = "plot1.png", type = "cairo")
# Output in your own folder:

p1
dev.off()

2

#ggsave(plot = p1, "p1.pdf", device = cairo_pdf)

# reprex 2 ----------------------------------------------------------------
dat <- data.frame(
  x = c(1, 1.3, 1.6),
  y = c(1, 1, 1),
  circle = c("yes", "yes", "no")
)

p2 <- ggplot() +
  coord_equal() +
  theme_classic() +
  geom_circle(
    data = subset(dat, circle == "yes"),
    aes(x0 = x, y0 = y, r = 0.5, alpha = circle),
    fill = "grey",
    color = NA,
    show.legend = TRUE
  ) %>% blend("source") +
  geom_point(
    data = dat,
    aes(x, y, color = circle)
  ) +
  scale_color_manual(
    values = c("yes" = "blue", "no" = "red")
  ) +
  scale_alpha_manual(
    values = c("yes" = 0.25, "no" = 0)
  )
#> Warning: Your graphics device, "quartz_off_screen", reports that blend = "source" is not supported.
#>  - If the blending output IS NOT as expected (e.g. geoms are not being
#>    drawn), then you must switch to a graphics device that supports
#>    blending, like png(type = "cairo"), svg(), or cairo_pdf().
#>  - If the blending output IS as expected despite this warning, this is
#>    likely a bug *in the graphics device*. Unfortunately, several
#>    graphics do not correctly report their capabilities. You may wish to
#>    a report a bug to the authors of the graphics device. In the mean
#>    time, you can disable this warning via options(ggblend.check_blend =
#>    FALSE).
#>  - For more information, see the Supported Devices section of
#>    help('blend').

png(filename = "plot2.png", type = "cairo")

# Output in your folder
p2

dev.off()
#ggsave(plot = p2, "p2.pdf", device = cairo_pdf)

^{创建于 2022-08-17，使用 reprex v2.0.2}

更新

您可以做的是使用 sf 包中的 st_union 对区域进行 UNION，这样您就可以得到一个区域，而不是像这样的重叠区域:

library(tidyverse)
library(sf)

dat <- tribble(
  ~xmin, ~xmax, ~ymin, ~ymax,
  10,    30,    10,    30,
  20,    40,    20,    40,
  15,    35,    15,    25,
  10,    15,    35,    40
)

area1 <- dat %>%
  slice(1) %>%
  as_vector() %>%
  st_bbox() %>%
  st_as_sfc()

area2 <- dat %>%
  slice(2) %>%
  as_vector() %>%
  st_bbox() %>%
  st_as_sfc()

area3 <- dat %>%
  slice(3) %>%
  as_vector() %>%
  st_bbox() %>%
  st_as_sfc()

area4 <- dat %>%
  slice(4) %>%
  as_vector() %>%
  st_bbox() %>%
  st_as_sfc()

all_areas <- st_union(area1, area2) %>%
  st_union(area3) %>%
  st_union(area4)

ggplot(all_areas) +
  geom_sf(alpha = 0.5, fill = "grey", colour = "grey") +
  theme(legend.position = "none")

ggplot(all_areas) +
  geom_sf(alpha = 0.8, fill = "grey", colour = "grey") +
  theme(legend.position = "none")

^{由 reprex package 于 2022-08-17 创建(v2.0.1)}

第一个答案

也许你想要这个，你可以使用 scale_alpha 和 range 和 limits 来保持相同的区域 alpha 像这样:

library(tidyverse)

dat <- tribble(
  ~xmin, ~xmax, ~ymin, ~ymax,
  10,    30,    10,    30,
  20,    40,    20,    40,
  15,    35,    15,    25,
  10,    15,    35,    40
)

ggplot() +
  geom_rect(data = dat,
            aes(
              xmin = xmin,
              xmax = xmax,
              ymin = ymin,
              ymax = ymax,
              alpha = 0.5
            )) +
  scale_alpha(range = c(0, 1), limits = c(0, 0.5)) +
  theme(legend.position = "none")

^{由 reprex package 于 2022-07-26 创建(v2.0.1)}