字符函数

字符串长度函数：
length()返回向量元素的个数、矩阵元素的个数、数据框字段数量和列表元素的个数

a <- rnorm(100)b <- matrix(1:12,ncol=3)cc <- irisdd <- list(a=c("a","b","c"),b=1:10,c=mtcars)length(a);length(b);length(cc);length(dd)

nchar()函数返回每个字符串的字符数

al <- state.namehead(al)[1] "Alabama"    "Alaska"     "Arizona"    "Arkansas"   "California" "Colorado"  nchar(head(al))[1]  7  6  7  8 10  8

cat()函数可以显示和连接字符串.该函数可以将字符串合并,并直接打印在屏幕中

 a=3cat("The answer is",a)  The answer is 3

cat()函数中使用”\n”参数为换行符，”\t”作为4个字节的空格

cat("my name is ","Gao Li")cat("my name is","\n","Guo Li")cat("my name is ","\t","Guo Li")cat("我们认识4年了","这4年过得如何？","有快乐的回忆","也有很多不愉快",fill=1)cat()函数中的参数file允许将输出结果指定到一个文件中

paste()函数可以连接字符串

paste("the answer is",a)#paste()函数在屏幕中输出带引号的字符串[1] "the answer is 3"paste("我的学校在","武汉-湖北",sep=":")paste(c("我的学校在","武汉-湖北"),sep=":") #sep参数对输入的向量不起作用paste(c("我的学校在","武汉-湖北"),collapse=":")

substring()或substr()函数获取字符串的子串,其中
first(start)和last(stop)参数可以是一个数值，也可以是一个向量.

substr("abcdef",2,4)#返回字符串"bcd"substring("abcdef",1:6,1:6)#一次提取一个字符[1] "a" "b" "c" "d" "e" "f"substr(rep("abcdef",4),1:4,4:5)#两个参数的长度不一样,短的会被循环[1] "abcd" "bcde" "cd"   "de"  x <- c("asfef", "qwerty", "yuiop[", "b", "stuff.blah.yech")substr(x, 2, 5)#提取字符向量中每一个字符串的特定字符[1] "sfef" "wert" "uiop" ""     "tuff"substring(x, 2, 4:6)[1] "sfe"   "wert"  "uiop[" ""      "tuff" #寻找字符串中特定字符的未知#将字符串转换为字符向量text1 <- "my name is Gao Li"n <- nchar(text1)str_value <- substring(text1,1:n,1:n)#  which()函数确定某个字符的位置which(str_value=="G")