合并：‘NA’，‘NA’在结果中被复制

Question

我正在查看此链接中的示例代码。

http://www.milanor.net/blog/maps-in-r-plotting-data-points-on-a-map/

数据集的位置似乎有变化，所以我稍微修改了代码以适应。

airports <- read.delim("https://raw.githubusercontent.com/jpatokal/openflights/master/data/airports.dat", sep=",")
colnames(airports) <- c("ID", "name", "city", "country", "IATA_FAA", "ICAO", "lat", "lon", "altitude", "timezone", "DST")
head(airports)

library(rworldmap)
newmap <- getMap(resolution = "low")
plot(newmap, xlim = c(-20, 59), ylim = c(35, 71), asp = 1)
points(airports$lon, airports$lat, col = "red", cex = .6)



routes <- read.csv("https://raw.githubusercontent.com/jpatokal/openflights/master/data/routes.dat", header=F)
colnames(routes) <- c("airline", "airlineID", "sourceAirport", "sourceAirportID", "destinationAirport", "destinationAirportID", "codeshare", "stops", "equipment")
head(routes)

library(plyr)
departures <- ddply(routes, .(sourceAirportID), "nrow")
names(departures)[2] <- "flights"
arrivals <- ddply(routes, .(destinationAirportID), "nrow")
names(arrivals)[2] <- "flights"

这一切似乎都很好。下面的代码似乎是关闭的，但我不知道为什么。

airportD <- merge(airports, departures, by.x = "ID", by.y = "sourceAirportID")
airportA <- merge(airports, arrivals, by.x = "ID", by.y = "destinationAirportID")

我得到了一个错误：

警告信息:在merge.data.frame中(机场、起飞，In .x= "ID"，in .y= "sourceAirportID")：列名‘NA’，‘NA’在结果中重复 警告信息:在merge.data.frame(机场，到达者，In .x= "ID"，in .y= "destinationAirportID")：列名‘NA’，‘NA’在结果中重复

我做错了什么？

Answer 1

首先，这些只是警告，而不是错误。也就是说，一切仍然正常，但可能不是预期的那样。这个问题产生于

colnames(airports) <- c("ID", "name", "city", "country", "IATA_FAA", "ICAO", "lat", "lon", "altitude", "timezone", "DST")

其中只指定11个列名，而有14个列。因此，有三列被命名为NA，这对于merge来说是一个潜在的问题。

如果结果(即airportD和airportA)是预期的，则不需要更改任何内容。不过，最好给这三列取适当的列名。