【发布时间】：2012-10-05 15:14:05
【问题描述】：
我正在尝试将数据框中的列设置为“美国”或“外国”，具体取决于国家/地区。我相信这样做的正确方法是编写一个函数，然后使用sapply 来实际更新数据帧。这是我第一次在R 中尝试这样的事情——在SQL 中，我会写一个UPDATE 查询。
这是我的数据框：
str(clients)
'data.frame': 252774 obs. of 4 variables:
$ ClientID : Factor w/ 252774 levels "58187855","59210128",..: 19 20 21 22 23 24 25 26 27 28 ...
$ Country : Factor w/ 207 levels "Afghanistan",..: 196 60 139 196 196 40 40 196 196 196 ...
$ CountryType : chr "" "" "" "" ...
$ OrderSize : num 12.95 21.99 5.00 7.50 44.5 ...
head(clients)
ClientID Country CountryType OrderSize
1 58187855 United States 12.95
2 59210128 France 21.99
3 65729284 Pakistan 5.00
4 25819711 United States 7.50
5 62837458 United States 44.55
6 88379852 China 99.28
我试图写的函数是这样的：
updateCountry <- function(x) {
if (clients$Country == "US") {
clients$CountryType <- "US"
} else {
clients$CountryType <- "Foreign"
}
}
然后我会像这样应用它：
sapply(clients, updateCountry)
当我对数据帧的头部运行sapply 时，我得到了这个：
"US" "US" "US" "US" "US" "US"
Warning messages:
1: In if (clients$Country == "United States") { :
the condition has length > 1 and only the first element will be used
2: In if (clients$Country == "United States") { :
the condition has length > 1 and only the first element will be used
3: In if (clients$Country == "United States") { :
the condition has length > 1 and only the first element will be used
4: In if (clients$Country == "United States") { :
the condition has length > 1 and only the first element will be used
5: In if (clients$Country == "United States") { :
the condition has length > 1 and only the first element will be used
6: In if (clients$Country == "United States") { :
the condition has length > 1 and only the first element will be used
该函数似乎正确地对 Country 进行了分类，但没有正确更新 clients$CountryType 列。我究竟做错了什么？另外 - 这是完成更新数据框的最佳方式吗？
【问题讨论】：