strsplit                package:base                R Documentation

_S_p_l_i_t _t_h_e _E_l_e_m_e_n_t_s _o_f _a _C_h_a_r_a_c_t_e_r _V_e_c_t_o_r

_D_e_s_c_r_i_p_t_i_o_n:

     Split the elements of a character vector 'x' into substrings
     according to the presence of substring 'split' within them.

_U_s_a_g_e:

     strsplit(x, split, extended = TRUE, fixed = FALSE, perl = FALSE)

_A_r_g_u_m_e_n_t_s:

       x: character vector, each element of which is to be split. 
          Other inputs, including a factor, will give an error. 

   split: character vector (or object which can be coerced to such)
          containing regular expression(s) (unless 'fixed = TRUE') to
          use for splitting.  If empty matches occur, in particular if
          'split' has length 0, 'x' is split into single characters. If
          'split' has length greater than 1, it is re-cycled along 'x'. 

extended: logical.  If 'TRUE', extended regular expression matching is
          used, and if 'FALSE' basic regular expressions are used. 

   fixed: logical.  If 'TRUE' match string exactly, otherwise use
          regular expressions.  Has priority over 'perl' and
          'extended'. 

    perl: logical.  Should perl-compatible regexps be used? Has
          priority over 'extended'. 

_D_e_t_a_i_l_s:

     Argument 'split' will be coerced to character, so you will see
     uses with 'split = NULL' to mean 'split = character(0)', including
     in the examples below.

     Note that splitting into single characters can be done _via_
     'split=character(0)' or 'split=""'; the two are equivalent. The
     definition of 'character' here depends on the locale (and perhaps
     OS): in a single-byte locale it is a byte, and in a multi-byte
     locale it is the unit represented by a 'wide character' (almost
     always a Unicode point).

     A missing value of 'split' does not split the corresponding
     element(s) of 'x' at all.

     The algorithm applied to each input string is


         repeat {
             if the string is empty
                 break.
             if there is a match
                 add the string to the left of the match to the output.
                 remove the match and all to the left of it.
             else
                 add the string to the output.
                 break.
         }

     Note that this means that if there is a match at the beginning of
     a (non-empty) string, the first element of the output is '""', but
     if there is a match at the end of the string, the output is the
     same as with the match removed.

_V_a_l_u_e:

     A list of length 'length(x)' the 'i'-th element of which contains
     the vector of splits of 'x[i]'.

_W_a_r_n_i_n_g:

     The standard regular expression code has been reported to be very
     slow when applied to extremely long character strings (tens of
     thousands of characters or more): the code used when 'perl = TRUE'
     seems much faster and more reliable for such usages.

     The 'perl = TRUE' option is only implemented for single-byte and
     UTF-8 encodings, and will warn if used in a non-UTF-8 multibyte
     locale.

_S_e_e _A_l_s_o:

     'paste' for the reverse, 'grep' and 'sub' for string search and
     manipulation; further 'nchar', 'substr'.

     regular expression for the details of the pattern specification.

_E_x_a_m_p_l_e_s:

     noquote(strsplit("A text I want to display with spaces", NULL)[[1]])

     x <- c(as = "asfef", qu = "qwerty", "yuiop[", "b", "stuff.blah.yech")
     # split x on the letter e
     strsplit(x,"e")

     unlist(strsplit("a.b.c", "."))
     ## [1] "" "" "" "" ""
     ## Note that 'split' is a regexp!
     ## If you really want to split on '.', use
     unlist(strsplit("a.b.c", "\\."))
     ## [1] "a" "b" "c"
     ## or
     unlist(strsplit("a.b.c", ".", fixed = TRUE))

     ## a useful function: rev() for strings
     strReverse <- function(x)
             sapply(lapply(strsplit(x, NULL), rev), paste, collapse="")
     strReverse(c("abc", "Statistics"))

     ## get the first names of the members of R-core
     a <- readLines(file.path(R.home("doc"),"AUTHORS"))[-(1:8)]
     a <- a[(0:2)-length(a)]
     (a <- sub(" .*","", a))
     # and reverse them
     strReverse(a)

     ## Note that final empty strings are not produced:
     strsplit(paste(c("", "a", ""), collapse="#"), split="#")[[1]]
     # [1] ""  "a"
     ## and also an empty string is only produced before a definite match:
     strsplit("", " ")[[1]]    # character(0)
     strsplit(" ", " ")[[1]]   # [1] ""

