在R中从多数据框自动生成绘图的问题求助

问题描述 #

作为R语言新手，我拥有四个数据框df_wspr_40、df_wspr_60、df_wspr_80、df_wspr_160，希望为它们生成相同样式的绘图。另有存储这些数据框名称数字部分的列表band：

> band 
[[1]]
[1] 40

[[2]]
[1] 60

[[3]]
[1] 80

[[4]]
[1] 160 

尝试用for循环批量生成绘图，但无法让ggplot正确调用对应的数据框，原代码如下：

for (x in band) {
  current.df = paste("df_wspr_", x, sep="")

  plot.subtitle = paste(x,"m Band from ",first_row," to ",last_row, sep = "")
    
  pl_dis_wspr <- ggplot(data=current.df, aes(y=avg_distance,x=date_120_min_interval)) +
    geom_bar(stat="identity", width = 0.5, position = position_dodge (0.8)) +
    geom_smooth(aes(group = 1), linewidth = 1, method = "loess", se = TRUE) +
    labs(x="Date & Time", y = "Distance Km", title = "120 minute Average Distance", subtitle = plot.subtitle) +
    theme(axis.text.x = element_blank())
  pl_dis_wspr
  
} 

问题原因 #

paste("df_wspr_", x, sep="")生成的是字符串（比如"df_wspr_40"），但ggplot()的data参数需要传入实际的数据框对象，而非字符串形式的名称，因此无法识别对应的数据。

两种解决方法 #

方法1：使用get()函数获取数据框对象 #

get()函数可以根据字符串名称找到环境中对应的对象，修改循环中获取数据框的代码即可：

for (x in band) {
  # 将字符串转为数据框对象
  current.df <- get(paste("df_wspr_", x, sep=""))

  plot.subtitle <- paste(x,"m Band from ", first_row," to ", last_row, sep = "")
    
  pl_dis_wspr <- ggplot(data=current.df, aes(y=avg_distance, x=date_120_min_interval)) +
    geom_bar(stat="identity", width = 0.5, position = position_dodge(0.8)) +
    geom_smooth(aes(group = 1), linewidth = 1, method = "loess", se = TRUE) +
    labs(x="Date & Time", y = "Distance Km", title = "120 minute Average Distance", subtitle = plot.subtitle) +
    theme(axis.text.x = element_blank())
  
  # 显式打印绘图（脚本中必须添加，RStudio交互式环境可省略）
  print(pl_dis_wspr)
} 

方法2：将数据框存入列表（更规范的R编程风格） #

把分散的数据框统一存入列表，避免通过字符串名称调用，代码更易维护：

# 先创建包含所有数据框的列表
df_list <- list(
  "40" = df_wspr_40,
  "60" = df_wspr_60,
  "80" = df_wspr_80,
  "160" = df_wspr_160
)

# 遍历列表的频段名称和对应数据框
for (band_num in names(df_list)) {
  current.df <- df_list[[band_num]]
  plot.subtitle <- paste(band_num,"m Band from ", first_row," to ", last_row, sep = "")
    
  pl_dis_wspr <- ggplot(data=current.df, aes(y=avg_distance, x=date_120_min_interval)) +
    geom_bar(stat="identity", width = 0.5, position = position_dodge(0.8)) +
    geom_smooth(aes(group = 1), linewidth = 1, method = "loess", se = TRUE) +
    labs(x="Date & Time", y = "Distance Km", title = "120 minute Average Distance", subtitle = plot.subtitle) +
    theme(axis.text.x = element_blank())
  
  print(pl_dis_wspr)
}

额外提示 #

如果需要保存所有生成的绘图，可以创建一个空列表，将每个绘图存入其中：

plot_list <- list()
for (x in band) {
  current.df <- get(paste("df_wspr_", x, sep=""))
  # ... 生成pl_dis_wspr的代码 ...
  plot_list[[as.character(x)]] <- pl_dis_wspr
}

之后可通过plot_list[["40"]]直接调用对应频段的绘图。

内容的提问来源于stack exchange，提问作者Sean Smith