8.13（R语言字符串的简单使用）

 rep(c(1,2,3),length.out=10)
 [1] 1 2 3 1 2 3 1 2 3 1
> rep(x = 1,... = 5)
[1] 1
> rep(x = 1,each=10)
 [1] 1 1 1 1 1 1 1 1 1 1
> rep(c(1,2,3),each=10)
 [1] 1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 3 3 3 3 3 3 3 3 3 3
> rep(c(1,2,3),times=10)
 [1] 1 2 3 1 2 3 1 2 3 1 2 3 1 2 3 1 2 3 1 2 3 1 2 3 1 2 3 1 2 3

> grep("[a-z]", letters)
 [1]  1  2  3  4  5  6  7  8  9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26
> letters
> grep("[b-c]", letters)
[1] 2 3
 [1] "a" "b" "c" "d" "e" "f" "g" "h" "i" "j" "k" "l" "m" "n" "o" "p" "q" "r" "s" "t"
[21] "u" "v" "w" "x" "y" "z"
> gsub("([ab])", "\\1_\\1_", "abc and ABC")
[1] "a_a_b_b_c a_a_nd ABC"
> grep("[a-b]", letters)
[1] 1 2

> x <- c("one","first")
> nchar(x)
[1] 3 5
> length(x)
[1] 2

> month.abb
 [1] "Jan" "Feb" "Mar" "Apr" "May" "Jun" "Jul" "Aug" "Sep" "Oct" "Nov" "Dec"
> nth
Error: object ‘nth‘ not found
> paste(month.abb, x, sep = ": ", collapse = "; ")
[1] "Jan: one; Feb: first; Mar: one; Apr: first; May: one; Jun: first; Jul: one; Aug: first; Sep: one; Oct: first; Nov: one; Dec: first"
> 

> substr(x,1,1)
[1] "o" "f"
> x
[1] "one"   "first"
> substr(month.abb,1,2)
 [1] "Ja" "Fe" "Ma" "Ap" "Ma" "Ju" "Ju" "Au" "Se" "Oc" "No" "De"

 toupper(substr(month.abb,1,2))
 [1] "JA" "FE" "MA" "AP" "MA" "JU" "JU" "AU" "SE" "OC" "NO" "DE"
> tolower(substr(month.abb,1,2))
 [1] "ja" "fe" "ma" "ap" "ma" "ju" "ju" "au" "se" "oc" "no" "de"

strsplit(x, "")
[[1]]
[1] "o" "n" "e"

[[2]]
[1] "f" "i" "r" "s" "t"

> a <- c(na,1:49)
Error: object ‘na‘ not found
> a <- c(NA,1:49)
> a
 [1] NA  1  2  3  4  5  6  7  8  9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26
[28] 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49
> sum(a.na.rm)
Error: object ‘a.na.rm‘ not found
> sum(a.na.rm=TRUE)
[1] 1
> sum(a,na.rm=TRUE)
[1] 1225
> is.na(a)
 [1]  TRUE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE
[14] FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE
[27] FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE
[40] FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE

> y <- c(1:5)
> outer(x,y,FUN ="paste")
     [,1]      [,2]      [,3]      [,4]      [,5]     
[1,] "one 1"   "one 2"   "one 3"   "one 4"   "one 5"  
[2,] "first 1" "first 2" "first 3" "first 4" "first 5"
> x
[1] "one"   "first"
> outer(y,x,FUN ="paste")
     [,1]    [,2]     
[1,] "1 one" "1 first"
[2,] "2 one" "2 first"
[3,] "3 one" "3 first"
[4,] "4 one" "4 first"
[5,] "5 one" "5 first"

> class(outer(y,x,FUN ="paste"))
[1] "matrix" "array" 
> class(paste(month.abb, x, sep = ": ", collapse = "; "))
[1] "character"