expression               package:base               R Documentation

_U_n_e_v_a_l_u_a_t_e_d _E_x_p_r_e_s_s_i_o_n_s

_D_e_s_c_r_i_p_t_i_o_n:

     Creates or tests for objects of mode '"expression"'.

_U_s_a_g_e:

     expression(...)

     is.expression(x)
     as.expression(x, ...)

_A_r_g_u_m_e_n_t_s:

     ...: valid R calls, symbols or constants.

       x: an arbitrary R object.

_D_e_t_a_i_l_s:

     'Expression' here is not being used in its colloquial sense, that
     of mathematical expressions.  Those are calls (see 'call') in R,
     and an R expression vector is a list of calls etc, typically as
     returned by 'parse'.

     As an object of mode '"expression"' is a list, it can be subsetted
     by both '[' and by '[[', the latter extracting individual calls.

_V_a_l_u_e:

     'expression' returns a vector of type '"expression"' containing
     its arguments (unevaluated).

     'is.expression' returns 'TRUE' if 'expr' is an expression object
     and 'FALSE' otherwise.

     'as.expression' attempts to coerce its argument into an expression
     object.

_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:

     'call', 'eval', 'function'. Further, 'text' and 'legend' for
     plotting mathematical expressions.

_E_x_a_m_p_l_e_s:

     length(ex1 <- expression(1+ 0:9))# 1
     ex1
     eval(ex1)# 1:10

     length(ex3 <- expression(u,v, 1+ 0:9))# 3
     mode(ex3 [3]) # expression
     mode(ex3[[3]])# call
     rm(ex3)

