[R] test if elements of a character vector contain letters

[Rui Barradas]

Hello,

Fun as an exercise in vectorization. 30 times faster. Don't look, guess.

Gave it up? Ok, here it is.


is_letter <- function(x, pattern=c(letters, LETTERS)){
     sapply(x, function(y){
         any(sapply(pattern, function(z) grepl(z, y, fixed=T)))
     })
}
# test ascii codes, just one loop.
has_letter <- function(x){
     sapply(x, function(y){
         y <- as.integer(charToRaw(y))
         any((65 <= y & y <= 90) | (97 <= y & y <= 122))
     })
}

x <- c(letters, 1:26)
x[1:10] <- paste(x[1:10], sample(1:10, 10), sep='')
x <- rep(x, 1e3)

t1 <- system.time(is_letter(x))
t2 <- system.time(has_letter(x))
rbind(t1, t2, t1/t2)
    user.self sys.self elapsed user.child sys.child
t1     15.69        0   15.74         NA        NA
t2      0.50        0    0.50         NA        NA
        31.38      NaN   31.48         NA        NA


Em 06-08-2012 17:25, Liviu Andronic escreveu:
> Dear all
> I'm pretty sure that I'm approaching the problem in a wrong way.
> Suppose the following character vector:
>> (x[1:10] <- paste(x[1:10], sample(1:10, 10), sep=''))
>   [1] "a10" "b7"  "c2"  "d3"  "e6"  "f1"  "g5"  "h8"  "i9"  "j4"
>> x
>   [1] "a10" "b7"  "c2"  "d3"  "e6"  "f1"  "g5"  "h8"  "i9"  "j4"  "k"
> "l"   "m"   "n"
> [15] "o"   "p"   "q"   "r"   "s"   "t"   "u"   "v"   "w"   "x"   "y"
> "z"   "1"   "2"
> [29] "3"   "4"   "5"   "6"   "7"   "8"   "9"   "10"  "11"  "12"  "13"
> "14"  "15"  "16"
> [43] "17"  "18"  "19"  "20"  "21"  "22"  "23"  "24"  "25"  "26"
>
>
> How do you test whether the elements of the vector contain at least
> one letter (or at least one digit) and obtain a logical vector of the
> same dimension? I came up with the following awkward function:
> is_letter <- function(x, pattern=c(letters, LETTERS)){
>      sapply(x, function(y){
>          any(sapply(pattern, function(z) grepl(z, y, fixed=T)))
>      })
> }
>
>> is_letter(x)
>    a10    b7    c2    d3    e6    f1    g5    h8    i9    j4     k
> l     m     n     o
>   TRUE  TRUE  TRUE  TRUE  TRUE  TRUE  TRUE  TRUE  TRUE  TRUE  TRUE
> TRUE  TRUE  TRUE  TRUE
>      p     q     r     s     t     u     v     w     x     y     z
> 1     2     3     4
>   TRUE  TRUE  TRUE  TRUE  TRUE  TRUE  TRUE  TRUE  TRUE  TRUE  TRUE
> FALSE FALSE FALSE FALSE
>      5     6     7     8     9    10    11    12    13    14    15
> 16    17    18    19
> FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE
> FALSE FALSE FALSE FALSE
>     20    21    22    23    24    25    26
> FALSE FALSE FALSE FALSE FALSE FALSE FALSE
>> is_letter(x, 0:9)  ##function slightly misnamed
>    a10    b7    c2    d3    e6    f1    g5    h8    i9    j4     k
> l     m     n     o
>   TRUE  TRUE  TRUE  TRUE  TRUE  TRUE  TRUE  TRUE  TRUE  TRUE FALSE
> FALSE FALSE FALSE FALSE
>      p     q     r     s     t     u     v     w     x     y     z
> 1     2     3     4
> FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE
> TRUE  TRUE  TRUE  TRUE
>      5     6     7     8     9    10    11    12    13    14    15
> 16    17    18    19
>   TRUE  TRUE  TRUE  TRUE  TRUE  TRUE  TRUE  TRUE  TRUE  TRUE  TRUE
> TRUE  TRUE  TRUE  TRUE
>     20    21    22    23    24    25    26
>   TRUE  TRUE  TRUE  TRUE  TRUE  TRUE  TRUE
>
>
> Is there a nicer way to do this? Regards
> Liviu
>
>