在图像层中设置不同的填充比例

Question

我将以mtcars数据集为例。我想基于填充颜色在一个变量（cyl）和另一个变量（hp）之间转换相同的数据点。但是，比例设定为4：335之间的整个范围。因此，当显示cyl时，所有点看起来都相同，因为它们的颜色被“压扁”，因为缺乏更好的术语，所以hp的上限。我想要发生的是，在填充圆柱体时的色标是4：8，当显示hp时是52：335。这是一个最小的例子

library(ggplot2)
library(gganimate)
library(RColorBrewer)
library(grDevices)

myPalette <- colorRampPalette(rev(brewer.pal(11, "Spectral")))

anim <- ggplot(mtcars, aes(mpg, disp)) +
  geom_point(shape = 21, colour = "black", size = 3, stroke = 0.5, show.legend = T, aes(fill = cyl)) +
  geom_point(shape = 21, colour = "black", size = 3, stroke = 0.5, show.legend = T, aes(fill = hp)) +
  scale_fill_gradientn(colours = myPalette(100))+
  transition_layers(layer_length = 1, transition_length = 2) +
  enter_fade() + enter_grow()

anim

Answer 1

一种选择是使用填充为一个变量，使用颜色为另一个，使用一些点形状使用填充和其他颜色的事实。我对结果并不是百分之百满意，可能需要进行一些调整才能获得匹配的磅值：

anim <- ggplot(mtcars, aes(mpg, disp)) +
    geom_point(shape = 16,  size = 3, show.legend = T, aes(colour = cyl)) +
    geom_point(shape = 21, size = 3, stroke = 0, show.legend = T, aes(fill = hp)) +
    scale_fill_gradientn(colours = myPalette(100))+
    scale_colour_gradientn(colours = myPalette(100))+
    transition_layers(layer_length = 1, transition_length = 2) +
    enter_fade() + enter_grow()

Answer 2

这是另一种方法。这里需要更多的预处理，但我认为这种方法仍然有一些价值，因为对于更广泛的用例，它更适合在> 2个变量之间进行转换。

定义新数据集，其中聚集的列和填充值缩放到公共范围（0-1）：

library(dplyr)

# modify dataset
mtcars2 <- mtcars %>%
  select(mpg, disp, cyl, hp) %>%
  tidyr::gather(key, value, -mpg, -disp) %>%
  group_by(key) %>%
  mutate(scaled.value = (value - min(value)) / diff(range(value))) %>%
  ungroup()

> head(mtcars2)
# A tibble: 6 x 5
    mpg  disp key   value scaled.value
  <dbl> <dbl> <chr> <dbl>        <dbl>
1  21     160 cyl       6          0.5
2  21     160 cyl       6          0.5
3  22.8   108 cyl       4          0  
4  21.4   258 cyl       6          0.5
5  18.7   360 cyl       8          1  
6  18.1   225 cyl       6          0.5

由于相同的图例比例将在动画期间应用于不同的值，因此我们需要不同的标签。我们可以在绘图中包含其他几何图层来模拟这个，同时抑制实际的填充图例。

# may need further tweaking, depending on the actual plot's dimensions; this worked
# sufficiently for me
legend.position <- c("xmin" = max(mtcars2$mpg) - 0.05 * diff(range(mtcars2$mpg)),
                     "xmax" = max(mtcars2$mpg) - 0.02 * diff(range(mtcars2$mpg)),
                     "ymin" = max(mtcars2$disp) - 0.2 * diff(range(mtcars2$disp)),
                     "ymax" = max(mtcars2$disp) - 0.01 * diff(range(mtcars2$disp)))

生成情节：

anim1 <- ggplot(mtcars2, aes(mpg, disp)) +
  geom_point(aes(fill = scaled.value, group = interaction(mpg, disp, scaled.value)),
             shape = 21, colour = "black", size = 3, stroke = 0.5) +

  # pseudo legend title
  geom_text(aes(x = legend.position[["xmin"]],
                y = legend.position[["ymax"]],
                label = key),
            vjust = -1, hjust = 0, check_overlap = TRUE) +
  # pseudo legend labels (tweak number of breaks, font size, etc., as needed)
  geom_text(data = . %>%
              group_by(key) %>%
              summarise(y = list(modelr::seq_range(scaled.value, n = 5)),
                        label = list(modelr::seq_range(value, n = 5))) %>%
              ungroup() %>%
              tidyr::unnest() %>%
              mutate(y = legend.position[["ymin"]] + 
                       y * (legend.position[["ymax"]] - legend.position[["ymin"]])),            
            aes(x = legend.position[["xmax"]], y = y, label = as.character(round(label))),
            hjust = 0, nudge_x = 0.5, size = 3, check_overlap = TRUE) +
  # pseudo colour bar
  annotation_custom(grob = grid::rasterGrob(rev(myPalette(100)),
                                            width = unit(1, "npc"), height = unit(1, "npc")),
                    xmin = legend.position[["xmin"]],
                    xmax = legend.position[["xmax"]],
                    ymin = legend.position[["ymin"]],
                    ymax = legend.position[["ymax"]]) +

  scale_fill_gradientn(colours = myPalette(100), guide = FALSE) +
  labs(title = "{closest_state}") +
  transition_states(key) +
  enter_fade() +
  enter_grow()

# reducing nframes to speed up the animation, since there are only two states anyway
animate(anim1, nframes = 20)