character                package:base                R Documentation

_C_h_a_r_a_c_t_e_r _V_e_c_t_o_r_s

_D_e_s_c_r_i_p_t_i_o_n:

     Create or test for objects of type '"character"'.

_U_s_a_g_e:

     character(length = 0)
     as.character(x, ...)
     is.character(x)

_A_r_g_u_m_e_n_t_s:

  length: desired length.

       x: object to be coerced or tested.

     ...: further arguments passed to or from other methods.

_D_e_t_a_i_l_s:

     'as.character' and 'is.character' are generic: you can write
     methods to handle specific classes of objects, see
     InternalMethods.  Further, for 'as.character' the default method
     calls 'as.vector', so dispatch is first on methods for
     'as.character' and then for methods for 'as.vector'.

     'as.character' represents real and complex numbers to 15
     significant digits (technically the compiler's setting of the ISO
     C constant 'DBL_DIG', which will be 15 on machines supporting
     IEC60559 arithmetic according to the C99 standard).  This ensures
     that all the digits in the result will be reliable (and not the
     result of representation error), but does mean that conversion to
     character and back to numeric may change the number.  If you want
     to convert numbers to character with the maximum possible
     precision, use 'format'.

     'as.character' and 'is.character' are primitive, so positional
     matching is used and any names of supplied arguments are ignored. 
     This may not be true of their methods.

_V_a_l_u_e:

     'character' creates a character vector of the specified length.
     The elements of the vector are all equal to '""'.

     'as.character' attempts to coerce its argument to character type;
     like 'as.vector' it strips attributes including names. For lists
     it deparses the elements individually, except that it extracts the
     first element of length-one character vectors.

     'is.character' returns 'TRUE' or 'FALSE' depending on whether its
     argument is of character type or not.

_N_o_t_e:

     'as.character' truncates components of language objects to 500
     characters (was about 70 before 1.3.1).

_R_e_f_e_r_e_n_c_e_s:

     Becker, R. A., Chambers, J. M. and Wilks, A. R. (1988) _The New S
     Language_. Wadsworth & Brooks/Cole.

_S_e_e _A_l_s_o:

     'paste', 'substr' and 'strsplit' for character concatenation and
     splitting, 'chartr' for character translation and casefolding
     (e.g., upper to lower case) and 'sub', 'grep' etc for string
     matching and substitutions.  Note that 'help.search(keyword =
     "character")' gives even more links. 'deparse', which is normally
     preferable to 'as.character' for language objects.

_E_x_a_m_p_l_e_s:

     form <- y ~ a + b + c
     as.character(form)  ## length 3
     deparse(form)       ## like the input

     a0 <- 11/999          # has a repeating decimal representation
     (a1 <- as.character(a0))
     format(a0, digits=16) # shows one more digit
     a2 <- as.numeric(a1)
     a2 - a0               # normally around -1e-17
     as.character(a2)      # normally different from a1
     print(c(a0, a2), digits = 16)

