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:

     Search for an R object of the given name on the search path.

_U_s_a_g_e:

     exists(x, where = NULL, envir = parent.frame(),
            frame = NULL, mode = "any", inherits = TRUE)

_A_r_g_u_m_e_n_t_s:

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

where, envir, frame: an environment to be searched.  By default this is
          the environment where the call to `envir' takes place.

    mode: the mode of interest for the object.

inherits: should the enclosing frames of the environment be inspected.

_D_e_t_a_i_l_s:

     This function looks to see if the name `x' has a value bound to
     it. If `inherits' is `TRUE' and a value is not found for `x', then
     the parent frames of `envir' are searched until the name `x' is
     encountered. Warning: This is the default behaviour for R but not
     for S.

     If `mode' is specified then only objects of that mode are sought.
     The function returns `TRUE' if the variable is encountered and
     `FALSE' if not.

     The `mode' includes collections such as `"numeric"' and
     `"function"': any member of the collection will suffice.

_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

