字符串
获取字符串长度
- nchar(“”)
函数nchar以一个字符串为参数，返回这个字符串中的字符数。不同于length()函数，length()函数返回一个向量的长度。
> nchar("xuptduxu")
[1] 8
> a<-c("happy","birthday","to","you")
> nchar(a)
[1] 5 8 2 3
> length("xuptduxu")
[1] 1
连接字符串
> paste("happy","birthday","to","you!")
[1] "happy birthday to you!"
> paste("happy","birthday","to","you!",sep = "")
[1] "happybirthdaytoyou!"
> paste("happy","birthday","to","you!",sep = "-")
[1] "happy-birthday-to-you!"
提取子串
- substr(string,start,end)函数：string原始字符串；提取开始于start，结束于end的子串
> substr("xuptduxu",5,8)
[1] "duxu"
> ss<-c("Moe","Larry","Curly")
> substr(ss,1,3)
[1] "Moe" "Lar" "Cur"
> cities<-c("New York, NY","Los Angeles, CA","Peoria, IL")
> substr(cities,nchar(cities)-1,nchar(cities))
[1] "NY" "CA" "IL"
根据分隔符分割字符串
- strsplit(string,delimiter)函数：将一个字符串分割为多个子串，子串之间用分隔符分开；delimiter可以是一个简单的字符串或者一个正则表达式；该函数返回一个列表
> path<-"/home/mike/data/trials.csv"
> strsplit(path,"/")
[[1]]
[1] "" "home" "mike" "data" "trials.csv"
替代子串
- sub(old,new,string)函数：替代字符串的第一个子串实例
- gsub(old,new,string)函数：替代字符串的所有子串实例
> s<-"Curly is the smart one.Curly is funny,too."
> sub("Curly","Moe",s)
[1] "Moe is the smart one.Curly is funny,too."
> gsub("Curly","Moe",s)
[1] "Moe is the smart one.Moe is funny,too."
> sub(" and SAS.","","You need R and SAS.")
[1] "You need R"
生成字符串的所有成对组合
- outer(strings1,strings2,paste,sep=”“)函数：结果是一个矩阵
> year<-c("2000","2001","2002","2003")
> month<-c("1","2","3","4","5","6")
> outer(year,month,paste,sep="-")
[,1] [,2] [,3] [,4] [,5] [,6]
[1,] "2000-1" "2000-2" "2000-3" "2000-4" "2000-5" "2000-6"
[2,] "2001-1" "2001-2" "2001-3" "2001-4" "2001-5" "2001-6"
[3,] "2002-1" "2002-2" "2002-3" "2002-4" "2002-5" "2002-6"
[4,] "2003-1" "2003-2" "2003-3" "2003-4" "2003-5" "2003-6"
得到当前日期
> Sys.Date()
[1] "2016-05-20"
