R语言入门学习2——字符型向量

as.character(x) 将其他类型的对象想转换为字符型

> x<-c(1:5)  #数值型
> x
[1] 1 2 3 4 5
> as.character(x)    #转换后变为字符型
[1] "1" "2" "3" "4" "5"

is.character(x)判断x是否为字符型

> is.character(x) 
[1] FALSE

nchar()函数，提取字符向量中字符串的个数

> y<-c("wo","shi","yi","zhi","ke","yan","gou")
> y
[1] "wo"  "shi" "yi"  "zhi" "ke"  "yan" "gou"
> nchar(y)
[1] 2 3 2 3 2 3 3

substr()函数或substring()函数，提取或替换字符型向量的部分子串

#（1）substr(x,start,stop)。
> substr(y,2,4)  #每个分量分别取2:4的字符
[1] "o"  "hi" "i"  "hi" "e"  "an" "ou"

> substr("abcdef",2,4)  #取第2到4个字符串
[1] "bcd"

#（2）substring(text,first,last)
> substring("abcdef",1:4,1:4)  #可以获取单个字符
[1] "a" "b" "c" "d"

> substring("abcdef",1:4,4) #字符数逐渐减少
[1] "abcd" "bcd"  "cd"   "d"   

strsplit()函数，将字符串分解，返回格式为列表格式

strsplit(x, split)， split为分隔的符号，字母等

> y<-c("wo shi yi zhi ke yan gou")
> y
[1] "wo shi yi zhi ke yan gou"
>  strsplit(y,split=" ")
[[1]]
[1] "wo"  "shi" "yi"  "zhi" "ke"  "yan" "gou"

> unlist(strsplit(y,split=" "))  #取消列表功能
[1] "wo"  "shi" "yi"  "zhi" "ke"  "yan" "gou"

>  strsplit(y,split="i")
[[1]]
[1] "wo sh"       " y"          " zh"         " ke yan gou"

paste()或paste0()函数，将多个对象连接在一块构成一个对象

paste(x,y,z,sep=" ") sep为分隔符，默认为空格

> paste("wo","shi")
[1] "wo shi"
> paste("wo","shi",sep="/")
[1] "wo/shi"

paste0(x,y),直接将对象连接，中间无分隔符,等同于paste(x,y,sep="")

> paste0("wo","shi")
[1] "woshi"

> paste("wo","shi",sep="")
[1] "woshi"

> x<-"file"
> y<-c(1:4)
> paste(x,y,sep=".")
[1] "file.1" "file.2" "file.3" "file.4"

noquote()函数，去掉字符型向量中的引号

> y<-c("wo","shi","yi","zhi","ke","yan","gou")
> noquote(y)
[1] wo  shi yi  zhi ke  yan gou

字符串大小写转换

toupper，转化为大写字母
tolower，转化为小写字母

> toupper(y)
[1] "WO"  "SHI" "YI"  "ZHI" "KE"  "YAN" "GOU"
> tolower("WOSHIYIZHIKEYANGOU")
[1] "woshiyizhikeyangou"