facet_grid中的免费色标 [英] Free colour scales in facet_grid

问题描述

说我有以下数据框:

# Set seed for RNG
set.seed(33550336)

# Create toy data frame
loc_x <- c(a = 1, b = 2, c = 3)
loc_y <- c(a = 3, b = 2, c = 1)
scaling <- c(temp = 100, sal = 10, chl = 1) 

df <- expand.grid(loc_name = letters[1:3], 
                  variables = c("temp", "sal", "chl"), 
                  season = c("spring", "autumn")) %>% 
  mutate(loc_x = loc_x[loc_name],
         loc_y = loc_y[loc_name],
         value = runif(nrow(.)),
         value = value * scaling[variables])

看起来像

# > head(df)
#   loc_name variables season loc_x loc_y     value
# 1        a      temp spring     1     3 86.364697
# 2        b      temp spring     2     2 35.222573
# 3        c      temp spring     3     1 52.574082
# 4        a       sal spring     1     3  0.667227
# 5        b       sal spring     2     2  3.751383
# 6        c       sal spring     3     1  9.197086

我想使用variables和season将这些数据绘制在构面网格中，以定义面板，如下所示:

I want to plot these data in a facet grid using variables and season to define panels, like this:

g <- ggplot(df) + geom_point(aes(x = loc_name, y = value), size = 5)
g <- g + facet_grid(variables ~ season) 
g

如您所见，不同的variables具有不同的音阶.所以，我用scales = "free"来解决这个问题.

As you can see, different variables have very different scales. So, I use scales = "free" to account for this.

g <- ggplot(df) + geom_point(aes(x = loc_name, y = value), size = 5)
g <- g + facet_grid(variables ~ season, scales = "free") 
g

非常方便.现在，说我想这样做，但是用loc_x和loc_y绘制点，并用颜色而不是y位置表示value:

Mucho convenient. Now, say I want to do this, but plot the points by loc_x and loc_y and have value represented by colour instead of y position:

g <- ggplot(df) + geom_point(aes(x = loc_x, y = loc_y, colour = value), 
                             size = 5)
g <- g + facet_grid(variables ~ season, scales = "free") 
g <- g + scale_colour_gradient2(low = "#3366CC", 
                                mid = "white", 
                                high = "#FF3300", 
                                midpoint = 50) 
g

请注意，颜色刻度不是免费的，并且像第一个数字一样，sal和chl的值不易读取.

Notice that the colour scales are not free and, like the first figure, values for sal and chl cannot be read easily.

我的问题:是否可以做等价于scales = "free"的方法，但是对于颜色，以便每一行(在这种情况下)都有一个单独的颜色条?或者，我是否必须绘制每个变量(即图中的行)并使用诸如cowplot之类的东西将它们修补在一起?

My question: is it possible to do an equivalent of scales = "free" but for colour, so that each row (in this case) has a separate colour bar? Or, do I have to plot each variable (i.e., row in the figure) and patch them together using something like cowplot?

推荐答案

使用dplyr的开发版本:

library(dplyr)
library(purrr)
library(ggplot2)
library(cowplot)

df %>% 
  group_split(variables, season) %>% 
  map(
    ~ggplot(., aes(loc_x, loc_y, color = value)) + 
      geom_point(size = 5) +
      scale_colour_gradient2(
        low = "#3366CC", 
        mid = "white", 
        high = "#FF3300", 
        midpoint = median(.$value)
      ) +
      facet_grid(~ variables + season, labeller = function(x) label_value(x, multi_line = FALSE))
  ) %>% 
  plot_grid(plotlist = ., align = 'hv', ncol = 2)

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