ggplot里面的for循环

Question

我想遍历六个相似的数据框并使用 ggplot 打印出六个图。

我的代码在我单独运行绘图时有效，但我无法使用 for 循环让 ggplot 运行六次。我的六个数据框是 gg_pets 中列出的六种动物。

cat <- data.frame(Breed = c("American Shorthair","Ragdoll","Persian","Sphynx","Maine Coon"), 
Longevity = c("17","19","15","17","20"))

dog <- data.frame(Breed = c("Havanese","Bulldog","Beagle","Chihuahua","Poodle"), 
Longevity = c("20","11","12","15","16"))

#etc for types of birds, fish, snakes, and ferrets

#the following works
plot <- ggplot(data = cat, aes(x = Breed, y = Longevity, fill = Breed)) + 
  geom_bar(stat = "identity", position = position_dodge()) +
  xlab("Breed") +
  ylab("Longevity") +
  ggtitle("cat") +
  geom_text(aes(label = Longevity), vjust = -0.3, color = "black", size = 3.5) +
  theme(axis.line = element_line(color = "black"), axis.text = element_text(color = "black"), 
        legend.position = "none", plot.title = element_text(hjust = .5),
        panel.grid.minor = element_blank(), panel.grid.major = element_blank(),
        panel.border = element_rect(color = "black", fill = NA, size = 0.8),
        panel.background = element_rect(fill = NA), text = element_text(size=10))
print(plot)

gg_pets <- c("cat","dog","bird","fish","snake","ferret")

#the following does not work
for (i in 1:length(gg_pets)){
    plot <- ggplot(data = [i], aes(x = Breed, y = Longevity, fill = Breed)) + 
    geom_bar(stat = "identity", position = position_dodge()) +
    xlab("Breed") +
    ylab("Longevity") +
    ggtitle([i]) +
    geom_text(aes(label = Longevity), vjust = -0.3, color = "black", size = 3.5) +
    theme(axis.line = element_line(color = "black"), axis.text = element_text(color = "black"), 
          legend.position = "none", plot.title = element_text(hjust = .5),
          panel.grid.minor = element_blank(), panel.grid.major = element_blank(),
          panel.border = element_rect(color = "black", fill = NA, size = 0.8),
          panel.background = element_rect(fill = NA), text = element_text(size=10))
    print(plot)
}

Answer 1

在您的示例中，gg_pets 只是一个字符串向量。您需要连接数据帧以便在 for 循环中对其进行迭代。你可以用一个列表来做。如下。您可以使用项目的名称作为标题。

...
gg_pets <- list(cat=cat, dog=dog)

#the following does not work
for (i in 1:length(gg_pets)) {
  plot <- ggplot(data = gg_pets[[i]], aes(x = Breed, y = Longevity, fill = Breed)) + 
    geom_bar(stat = "identity", position = position_dodge()) +
    xlab("Breed") +
    ylab("Longevity") +
    ggtitle(names(gg_pets)[i]) +
    geom_text(aes(label = Longevity), vjust = -0.3, color = "black", size = 3.5) +
    theme(axis.line = element_line(color = "black"), axis.text = element_text(color = "black"), 
          legend.position = "none", plot.title = element_text(hjust = .5),
          panel.grid.minor = element_blank(), panel.grid.major = element_blank(),
          panel.border = element_rect(color = "black", fill = NA, size = 0.8),
          panel.background = element_rect(fill = NA), text = element_text(size=10))
  print(plot)
}

Answer 2

我认为你需要

ggplot(data = get(i), ...)

但将数据集放在命名列表（my_data_list <- list(cat=cat, dog=dog, ...) 甚至 my_data_list <- mget(gg_pets)）中并使用 data = my_data_list[[i]] 可能会更惯用/更好的做法...

Answer 3

其他答案中提到的list 方法的替代方法是首先将所有内容都放在相同的data.frame 中，因为显然所有表都具有相同的变量；然后再有一个变量表示观察对应的是哪种宠物。如下：

pets_df <- bind_rows(cat %>% add_column(pet = 'cat'),
                     dog %>% add_column(pet = 'dog'))

> pets_df
                Breed Longevity pet
1  American Shorthair        17 cat
2             Ragdoll        19 cat
3             Persian        15 cat
4              Sphynx        17 cat
5          Maine Coon        20 cat
6            Havanese        20 dog
7             Bulldog        11 dog
8              Beagle        12 dog
9           Chihuahua        15 dog
10             Poodle        16 dog

然后，在循环的每次迭代中，您只需过滤data.frame。例如：

for (i in 1:length(gg_pets)) {
  plot <- ggplot(data = filter(pets_df, pet == gg_pets[i]), 
                 aes(x = Breed, y = Longevity, fill = Breed)) + 
    geom_bar(stat = "identity", position = position_dodge()) +
    xlab("Breed") +
    ylab("Longevity") +
    ggtitle(gg_pets[i]) +
    geom_text(aes(label = Longevity), vjust = -0.3, color = "black", size = 3.5) +
    theme(axis.line = element_line(color = "black"), axis.text = element_text(color = "black"), 
          legend.position = "none", plot.title = element_text(hjust = .5),
          panel.grid.minor = element_blank(), panel.grid.major = element_blank(),
          panel.border = element_rect(color = "black", fill = NA, size = 0.8),
          panel.background = element_rect(fill = NA), text = element_text(size=10))
  print(plot)
}