do.call                 package:base                 R Documentation

_E_x_e_c_u_t_e _a _F_u_n_c_t_i_o_n _C_a_l_l

_D_e_s_c_r_i_p_t_i_o_n:

     'do.call' constructs and executes a function call from a name or a
     function and a list of arguments to be passed to it.

_U_s_a_g_e:

     do.call(what, args, quote = FALSE, envir = parent.frame())

_A_r_g_u_m_e_n_t_s:

    what: either a function or a character string naming the function
          to be called.

    args: a _list_ of arguments to the function call.  The 'names'
          attribute of 'args' gives the argument names.

   quote: a logical value indicating whether to quote the arguments.

   envir: an environment within which to evaluate the call.  This will
          be most useful if 'what' is a character string and the
          arguments are symbols or quoted expressions.

_D_e_t_a_i_l_s:

     If 'quote' is 'FALSE', the default, then the arguments are
     evaluated (in the calling environment, not 'envir'.).  If 'quote'
     is 'TRUE' then each argument is quoted (see 'quote') so that the
     effect of argument evaluation is to remove the quote - leaving the
     original argument unevaluated when the call is constructed.

     The behavior of some functions, such as 'substitute', will not be
     the same for functions evaluated using 'do.call' as if they were
     evaluated from the interpreter.  The precise semantics are
     currently undefined and subject to change.

_V_a_l_u_e:

     The result of the (evaluated) function call.

_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' which creates an unevaluated call.

_E_x_a_m_p_l_e_s:

     do.call("complex", list(imag = 1:3))

     ## if we already have a list (e.g. a data frame)
     ## we need c() to add further arguments
     tmp <- expand.grid(letters[1:2], 1:3, c("+", "-"))
     do.call("paste", c(tmp, sep=""))

     do.call(paste, list(as.name("A"), as.name("B")), quote=TRUE)

     ## examples of where objects will be found.
     A <- 2
     f <- function(x) print(x^2)
     env <- new.env()
     assign("A", 10, envir = env)
     assign("f", f, envir = env)
     f <- function(x) print(x)
     f(A)                                    # 2
     do.call("f", list(A))                   # 2
     do.call("f", list(A), envir=env)        # 4
     do.call(f, list(A), envir=env)          # 2
     do.call("f", list(quote(A)), envir=env) # 100
     do.call(f, list(quote(A)), envir=env)   # 10
     do.call("f", list(as.name("A")), envir=env) # 100

     eval(call("f", A))                      # 2
     eval(call("f", quote(A)))               # 2
     eval(call("f", A), envir=env)           # 4
     eval(call("f", quote(A)), envir=env)    # 100

