在1张地图上绘制多条线

Question

我想在1张地图上绘制2条不同的路线。这是我作为例子的代码：

### Plot 2 routes on 1 map

# libraries

library(ggmap)
library(ggplot2)

# plot map

basicmap <- get_map(location = c(lon = 3, lat = 50),
                    zoom = 12,
                    maptype = "roadmap",
                    source = "google",
                    color = "color")  #completely random location
basicmap <- ggmap(basicmap)

# determine routes

routes <- data.frame(from = c("Rocquigny", "Nurlu"),
                     to = c("Heudicourt","Longavesnes"),
                     stringsAsFactors = FALSE)

# calculate routes

calculationroute <- function(startingpoint, stoppoint) {
  route(from = startingpoint,
        to = stoppoint,
        mode = "bicycling",
        structure = "route")
}
  #this function calculates the route

calculatedroutes <- mapply(calculationroute,
                           startingpoint = routes$from,
                           stoppoint = routes$to,
                           SIMPLIFY = FALSE)
  #calculate the 2 routes

# draw routes

drawroute <- function(route) {
  geom_path(aes(data = route,
                x = lon,
                y = lat))
}
  #this functions draws the route

extendedmap <- basicmap + lapply(X = calculatedroutes,
                                 FUN = drawroute)
plot(extendedmap)
  #draw the routes

所以这些是我采取的步骤：

1. 创建背景地图
2. 我创建了一个包含2条路线的起点和终点的数据框
3. 使用ggmap我计算这些路线的分段。
4. 我尝试在背景地图上绘制路线

可悲的是，最后一步失败并发生此错误：

Don't know how to automatically pick scale for object of type function. Defaulting to continuous
Error in data.frame(x = c(2.89030838012694, 3.11003494262694, 2.89030838012694,  : 
  arguments imply differing number of rows: 4, 0

我进行了搜索，this previous question想要做同样的事情。他最终选择的解决方案使用了for循环，而我宁愿使用lapply来保持代码的一致性。

Answer 1

正如我在评论中所说，label循环有效，但您可以采用更for种方式执行此操作。首先，我们需要更改您的ggplot调用，因为范围对于您的某条路线来说不够大：

ggmap

计算出路线后，我们可以制作一个长数据框：

basicmap <- get_map(location = c(lon = 3, lat = 50),
                    zoom = 8,
                    maptype = "roadmap",
                    source = "google",
                    color = "color")  #completely random location
basicmap <- ggmap(basicmap)

然后对do.call(rbind.data.frame, lapply(names(calculatedroutes), function(x) { cbind.data.frame(route=x, calculatedroutes[[x]], stringsAsFactors=FALSE) })) -> long_routes 使用group美学：

geom_path