R:字符串上的ifelse

Question

我正在根据另一个变量的字符串条件填充数据框的新变量.我收到以下错误消息:

Error in Source == "httpWWW.BGDAILYNEWS.COM" | Source == : operations are possible only for numeric, logical or complex types

我的代码如下:

County <- ifelse(Source == 'httpWWW.BGDAILYNEWS.COM' | 'WWW.BGDAILYNEWS.COM', 'Warren', ifelse(Source == 'httpWWW.HCLOCAL.COM' | 'WWW.HCLOCAL.COM', 'Henry', ifelse(Source == 'httpWWW.KENTUCKY.COM' | 'WWW.KENTUCKY.COM', 'Fayette', ifelse(Source == 'httpWWW.KENTUCKYNEWERA.COM' | 'WWW.KENTUCKYNEWERA.COM', 'Christian') )))

Answer 1

我建议你将深层嵌套的ifelse语句分解为更易于管理的块.

但错误告诉你,你不能那样使用|. 'a' | 'b'因为它是一个逻辑比较,所以没有意义.而是使用%in%:

Source %in% c('htpWWW.BGDAILYNEWS.com', 'WWW.BGDAILYNEWS.COM')

我想...如果我理解你在做什么,你会更好地使用多个作业:

County = vector(mode='character', length=length(Source))
County[County %in% c('htpWWW.BGDAILYNEWS.com', 'WWW.BGDAILYNEWS.COM')] <- 'Warren'
etc.

您还可以switch对此类事物使用语句:

myfun <- function(x) {
  switch(x,
         'httpWWW.BGDAILYNEWS.COM'='Warren',
         'httpWWW.HCLOCAL.COM'='Henry',
         etc...)
}

然后你想做一个简单的apply(sapply)传递每个元素Source到myfun:

County = sapply(Source, myfun)

或者最后,你可以使用factors和levels,但我会将其作为练习留给读者......

Answer 2

一种不同的方法:

county <- c("Warren","Henry","Fayette","Christian")
sites <- c("WWW.BGDAILYNEWS.COM","WWW.HCLOCAL.COM","WWW.KENTUCKY.COM","WWW.KENTUCKYNEWERA.COM")
County <- county[match(gsub("^http","",Source), sites)]

这将返回NA不匹配任何给定输入的字符串.

使用Hadley的建议(lookup-tables-character-subsetting):

lookup <- c(WWW.BGDAILYNEWS.COM="Warren", WWW.HCLOCAL.COM="Henry", WWW.KENTUCKY.COM="Fayette", WWW.KENTUCKYNEWERA.COM="Christian")
County <- unname(lookup[gsub("^http","",Source)])