从df中选择"europe"

Question

我的df2:

          League freq
18       England  108
27         Italy   79
20       Germany   74
43         Spain   64
19        France   49
39        Russia   34
31        Mexico   27
47        Turkey   24
32   Netherlands   23
37      Portugal   21
49 United States   18
29         Japan   16
25          Iran   15
7         Brazil   13
22        Greece   13
14         Costa   11
45   Switzerland   11
5        Belgium   10
17       Ecuador   10
23      Honduras   10
42   South Korea    9
2      Argentina    8
48       Ukraine    7
3      Australia    6
11         Chile    6
12         China    6
15       Croatia    6
35        Norway    6
41      Scotland    6
34       Nigeria    5

我试着选择europe.

europe <- subset(df2, nrow(x=18, 27, 20) select=c(1, 2))

什么是选择最有效的方式europe,africa,Asia...从df2？

Answer 1

您需要手动确定哪些国家/地区位于哪些国家/地区,或者您可以从某处获取此信息:

(使用XML包将html表刮到R数据帧的基本策略)

library(XML)
theurl <- "http://en.wikipedia.org/wiki/List_of_European_countries_by_area"
tables <- readHTMLTable(theurl)
library(stringr)
europe_names <- str_extract(as.character(tables[[1]]$Country),"[[:alpha:] ]+")
head(sort(europe_names))
## [1] "Albania"    "Andorra"    "Austria"    "Azerbaijan" "Belarus"     
## [6] "Belgium"   
## there's also a 'Total' entry in here but it's probably harmless ...
subset(df2,League %in% europe_names)

当然,你必须再次为亚洲,美国等来解决这个问题.