exists                 package:base                 R Documentation

_I_s _a_n _O_b_j_e_c_t _D_e_f_i_n_e_d?

_D_e_s_c_r_i_p_t_i_o_n:

     Look for an R object of the given name.

_U_s_a_g_e:

     exists(x, where = -1, envir = , frame, mode = "any", inherits = TRUE)

_A_r_g_u_m_e_n_t_s:

       x: a variable name (given as a character string).

   where: where to look for the object (see the details section); if
          omitted, the function will search as if the name of the
          object appeared unquoted in an expression.

   envir: an alternative way to specify an environment to look in, but
          it's usually simpler to just use the 'where' argument.

   frame: a frame in the calling list.  Equivalent to giving 'where' as
          'sys.frame(frame)'.

    mode: the mode of object sought.

inherits: should the enclosing frames of the environment be searched?

_D_e_t_a_i_l_s:

     The 'where' argument can specify the environment in which to look
     for the object in any of several ways: as an integer (the position
     in the 'search' list); as the character string name of an element
     in the search list; or as an 'environment' (including using
     'sys.frame' to access the currently active function calls).  The
     'envir' argument is an alternative way to specify an environment,
     but is primarily there for back compatibility.

     This function looks to see if the name 'x' has a value bound to it
     in the specified environment. If 'inherits' is 'TRUE' and a value
     is not found for 'x' in the specified environment, the enclosures
     of the environment are searched until the name 'x' is encountered.
      See 'environment' and the 'R Language Definition' manual for
     details about the structure of environments and their enclosures.

     *Warning:* 'inherits=TRUE' is the default behaviour for R but not
     for S.

     If 'mode' is specified then only objects of that mode are sought.
     The 'mode' may specify collections such as '"numeric"' and
     '"function"': any member of the collection will suffice.

_V_a_l_u_e:

     Logical, true if and only if an object of the correct name and
     mode is found.

_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:

     'get'.

_E_x_a_m_p_l_e_s:

     ##  Define a substitute function if necessary:
     if(!exists("some.fun", mode="function"))
       some.fun <- function(x) { cat("some.fun(x)\n"); x }
     search()
     exists("ls", 2) # true even though ls is in pos=3
     exists("ls", 2, inherits = FALSE) # false

