如何防止在ggplot2中停止额外几何图形更改关键alpha值？

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英文:

How can I stop additional geoms chaning the key alpha in ggplot2?

问题

我有两个使用部分透明颜色填充的ggplot2::geom_polygon图形。
我希望图例显示相同的透明度，但实际上它并没有。
理想的解决方案是，随着我添加具有相同填充和透明颜色的其他多边形，匹配的透明度也会缩放。

示例代码：

  1. chosen_alpha = 0.2
  2. ggplot() +
  3.     theme_minimal() +
  4.     geom_polygon(
  5.         aes(
  6.             fill = "A",
  7.             x = c(1, 2, 2),
  8.             y = c(1, 1, 2)
  9.         ),
  10.         alpha = chosen_alpha
  11.     ) +
  12.     geom_polygon(
  13.         aes(
  14.             fill = "A",
  15.             x = c(3, 4, 4),
  16.             y = c(3, 3, 4)
  17.         ),
  18.         alpha = chosen_alpha
  19.     ) +
  20.     guides(
  21.         fill = guide_legend(
  22.             override.aes = list(
  23.                 alpha = chosen_alpha
  24.             ),
  25.         )
  26.     )

如果我只有一个多边形，这是有效的，如下所示。

  1. chosen_alpha = 0.2
  2. ggplot() +
  3.     theme_minimal() +
  4.     geom_polygon(
  5.         aes(
  6.             fill = "A",
  7.             x = c(1, 2, 2),
  8.             y = c(1, 1, 2)
  9.         ),
  10.         alpha = chosen_alpha
  11.     ) +
  12.     guides(
  13.         fill = guide_legend(
  14.             override.aes = list(
  15.                 alpha = chosen_alpha
  16.             ),
  17.         )
  18.     )
英文:

I have two ggplot2::geom_pologons filled with a partially transparent colour.
I would like the key to display with the same alpha, but it does not.
The solution would ideally scale such that as I add additional polygons with the same fill and alpha colour the matching holds.

Example code:

  1. chosen_alpha = 0.2
  2. ggplot() +
  3.     theme_minimal() +
  4.     geom_polygon(
  5.         aes(
  6.             fill = "A",
  7.             x = c(1, 2, 2),
  8.             y = c(1, 1, 2)
  9.         ),
  10.         alpha = chosen_alpha
  11.     ) +
  12.     geom_polygon(
  13.         aes(
  14.             fill = "A",
  15.             x = c(3, 4, 4),
  16.             y = c(3, 3, 4)
  17.         ),
  18.         alpha = chosen_alpha
  19.     ) +
  20.     guides(
  21.         fill = guide_legend(
  22.             override.aes = list(
  23.                 alpha = chosen_alpha
  24.             ),
  25.         )
  26.     )

This does work if I only have one of the polygons, as follows.

  1. chosen_alpha = 0.2
  2. ggplot() +
  3.     theme_minimal() +
  4.     geom_polygon(
  5.         aes(
  6.             fill = "A",
  7.             x = c(1, 2, 2),
  8.             y = c(1, 1, 2)
  9.         ),
  10.         alpha = chosen_alpha
  11.     ) +
  12.     guides(
  13.         fill = guide_legend(
  14.             override.aes = list(
  15.                 alpha = chosen_alpha
  16.             ),
  17.         )
  18.     )

答案1

得分: 2

问题在于每个 geom 都会绘制一个键图形，也就是说，每添加一个 geom 就会有多个略微透明的矩形图层叠在一起，因此随着添加更多 geom，颜色会变得更加深色。

解决这个问题的最干净方法是只使用一个 geom_polygon 来绘制多边形。为此，将您的数据放入一个数据框中，并通过 group aes 来区分不同的多边形。

  1. library(ggplot2)
  3. chosen_alpha <- 0.2
  5. dat <- data.frame(
  6.   x = c(c(1, 2, 2), c(2, 3, 3)),
  7.   y = c(c(1, 1, 2), c(2, 2, 3)),
  8.   fill = "A",
  9.   group = rep(1:2, each = 3)
  10. )
  11. ggplot(dat) +
  12.   theme_minimal() +
  13.   geom_polygon(
  14.     aes(
  15.       fill = fill,
  16.       x = x,
  17.       y = y,
  18.       group = group
  19.     ),
  20.     alpha = chosen_alpha
  21.   )

第二个选项是将 key_glyph 设置为除一个 geom 之外的所有 geom 都为 "blank"。这样，键图形只会绘制一次：

  1. ggplot() +
  2.   theme_minimal() +
  3.   geom_polygon(
  4.     aes(
  5.       fill = "A",
  6.       x = c(1, 2, 2),
  7.       y = c(1, 1, 2)
  8.     ),
  9.     alpha = chosen_alpha,
  10.     key_glyph = "blank"
  11.   ) +
  12.   geom_polygon(
  13.     aes(
  14.       fill = "A",
  15.       x = c(2, 3, 3),
  16.       y = c(2, 2, 3)
  17.     ),
  18.     alpha = chosen_alpha
  19.   )

如何防止在ggplot2中停止额外几何图形更改关键alpha值？（第一种方法）

如何防止在ggplot2中停止额外几何图形更改关键alpha值？（第二种方法）

英文:

The issue is that for each geom a key glyph is drawn, i.e. you end up with multiple layers of slightly transparent rects which are drawn on top of each other and hence you end up with a darker color the more geoms are added.

The cleanest approach to fix your issue would be to use only one geom_polygon to draw your polygons. To this end put your data in a data.frame and account for the different polygons via the group aes.

  1. library(ggplot2)
  3. chosen_alpha &lt;- 0.2
  5. dat &lt;- data.frame(
  6.   x = c(c(1, 2, 2), c(2, 3, 3)),
  7.   y = c(c(1, 1, 2), c(2, 2, 3)),
  8.   fill = &quot;A&quot;,
  9.   group = rep(1:2, each = 3)
  10. )
  11. ggplot(dat) +
  12.   theme_minimal() +
  13.   geom_polygon(
  14.     aes(
  15.       fill = fill,
  16.       x = x,
  17.       y = y,
  18.       group = group
  19.     ),
  20.     alpha = chosen_alpha
  21.   )

如何防止在ggplot2中停止额外几何图形更改关键alpha值？<!-- -->

Second option would be to set the key_glyph to &quot;blank&quot; for all but one geom. This way the key glyph is only drawn once:

  1. ggplot() +
  2.   theme_minimal() +
  3.   geom_polygon(
  4.     aes(
  5.       fill = &quot;A&quot;,
  6.       x = c(1, 2, 2),
  7.       y = c(1, 1, 2)
  8.     ),
  9.     alpha = chosen_alpha,
  10.     key_glyph = &quot;blank&quot;
  11.   ) +
  12.   geom_polygon(
  13.     aes(
  14.       fill = &quot;A&quot;,
  15.       x = c(2, 3, 3),
  16.       y = c(2, 2, 3)
  17.     ),
  18.     alpha = chosen_alpha
  19.   )

如何防止在ggplot2中停止额外几何图形更改关键alpha值？<!-- -->

huangapple
  • 本文由 发表于 2023年8月10日 23:13:35
  • 转载请务必保留本文链接：https://go.coder-hub.com/76877094.html
  • ggplot2
  • r
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