R，获取城市的经度/纬度数据并将其添加到我的数据框中

Question

我想获取数据框中城市的经度/纬度数据，并在我的框架中添加2列。我是R的新手，我不知道该怎么做。 有人可以帮我这个

我的框架：

> data <- read.xlsx("example_city.xlsx", 1)
> data
        City Country
1  Stockholm  Sweden
2       Oslo  Norway
3       Rome   Italy
4       Rome   Italy
5  Stockholm  Sweden
6  Stockholm  Sweden
7      Paris  France
8      Paris  France
9    Hamburg Germany
10     Paris  France
11     Paris  France

Answer 1

参考原始问题https://stackoverflow.com/questions/20936263/use-ggplot2-to-plot-cities-on-a-map

# data 
cities <- sort(c(rep('Stockholm', 3), 'Oslo', 'Rome', 'Rome', 'Paris', rep('Bonn',10), 'Paris', 'Paris', 'Stockholm'))

# get frequencies
freq <- as.data.frame(table(cities))
library(plotrix)
freq$Freq <- rescale(freq$Freq, c(1,10)) # c(scale_min, scale_max)

# get cities latitude/longitude - kindly provided by google:
library(ggmap)
lonlat <- geocode(unique(cities)) 
cities <- cbind(freq, lonlat)

# get matches between names {maps} names and EU country names
library(maps)
eu <- c("Austria", "Belgium", "Bulgaria", "Croatia", "Cyprus", "Czech Republic", 
        "Denmark", "Estonia", "Finland", "France", "Germany", "Greece", 
        "Hungary", "Ireland", "Italy", "Latvia", "Lithuania", "Luxembourg", 
        "Malta", "Netherlands", "Poland", "Portugal", "Romania", "Slovakia", 
        "Slovenia", "Spain", "Sweden", "United Kingdom")
warning("No matches in database for ", paste(setdiff(eu, map_data('world')$region), collapse=", ")) 
europe <- map_data('world', region=eu)

# plot
library(ggplot2)
ggplot(europe, aes(x=long, y=lat, group=group)) +
  geom_polygon(fill="white", colour="black") +
  xlim(-20, 40) + ylim(25,75) +
  geom_point(data=cities, inherit.aes=F, aes(x=lon, y=lat, size=Freq), colour="red", alpha=.8) + 
  geom_text(data=cities, inherit.aes=F, aes(x=lon, y=lat, label=cities), vjust=1, colour="red", alpha=.5)