R - 在循环中保存多个图时出错

Question

我有一个像这个测试框架这样的数据框架，但要大得多。

lat_area = seq (50, 40, -0.5)
lon_area = seq (-10, 10, 0.5)
grid_area = matrix(0, ncol=2, nrow=length(lon_area)*length(lat_area))
grid_area[,2] = rep(lat_area, each=length(lon_area))
grid_area[,1] = lon_area
testframe = as.data.frame(grid_area)

colnames(testframe) = c("Lon", "Lat")
testframe$FDsw = rep(c(0.5,0.7), length.out= nrow(testframe))
testframe$Thgf = rep(c(0.2,0.3), length.out= nrow(testframe))
testframe$Igbff = rep(c(0.8,0.9), length.out= nrow(testframe))

我想为每个数据列制作等高线图（测试帧中的列 3:5） 我发现了多个关于如何自动保存多个图的问题。我认为最好的方法是将所有图保存在一个列表中，然后再从这个列表中保存它们。我的尝试在下面。

library(ggplot2)
library(metR)

plot_list = list()
for (i in 3:length(testframe)) {
  wd = map_data("world") 
  LP = ggplot() 
  LP = LP + 
    geom_contour_fill(data = testframe, aes(x = Lon, y = Lat, z = colnames(testframe)[i]), breaks = MakeBreaks(0.1)) + 
    geom_contour(data = testframe, aes(x = Lon, y = Lat, z = colnames(testframe)[i]), color = "blue", size = 0.6) + 
    geom_text_contour(data = testframe, aes(x = Lon, y = Lat, z = colnames(testframe)[i]), stroke = 0.1) + 
    scale_fill_divergent() +
    geom_polygon(data = wd , aes(x = long, y = lat, group = group), colour="black", fill = NA) + 
    coord_cartesian(xlim = c(-10, 10), ylim = c(50, 40)) +
    scale_x_longitude(ticks = 10)+ scale_y_latitude(ticks = 10) +
    labs(title= paste("Plot", colnames(testframe)[i], sep = " ")) 
  plot_list[[i]] = LP}

plot_list[1:2] = NULL
names(plot_list) = colnames(testframe)[3:ncol(testframe)]


for (i in 1:3) {
  file_name = paste("Plot", i, ".tiff", sep="")
  tiff(file_name)
  print(plot_list[[i]])
  dev.off()
}           

我不知道我做错了什么。我收到此错误：

Error in UseMethod("fullseq") : 
  no applicable method for 'fullseq' applied to an object of class "character"
In addition: Warning message:
In pretty.default(range(data$z, na.rm = TRUE), 10) :
  NAs introduced by coercion

有谁知道为什么这不起作用？

Answer 1

您不能将变量插入到常规的aes() 语句中，因为它们是在打印时进行评估的。您需要传递 sumbols 而不是字符串，并且变量未包含在绘图对象中。所以像

aes(x = Lon, y = Lat, z = colnames(testframe)[i])

行不通。使用最新版本的 ggplot2，您可以使用 rlang::sym() 和 !!（bang bang）运算符的组合将符号插入到表达式中。试试

aes(x = Lon, y = Lat, z = !!rlang::sym(colnames(testframe)[i]))