lapply                 package:base                 R Documentation

_A_p_p_l_y _a _F_u_n_c_t_i_o_n _o_v_e_r _a _L_i_s_t _o_r _V_e_c_t_o_r

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

     'lapply' returns a list of the same length as 'X'.  Each element
     of which is the result of applying 'FUN' to the corresponding
     element of 'X'.

     'sapply' is a "user-friendly" version of 'lapply' by default
     returning a vector or matrix if appropriate.

     'replicate' is a wrapper for the common use of 'sapply' for
     repeated evaluation of an expression (which will usually involve
     random number generation).

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

     lapply(X, FUN, ...)
     sapply(X, FUN, ..., simplify = TRUE, USE.NAMES = TRUE)

     replicate(n, expr, simplify = TRUE)

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

       X: list or (atomic) vector to be used.

     FUN: the function to be applied to each element of 'X'. In the
          case of functions like '+', '%*%', etc., the function name
          must be quoted.

     ...: optional arguments to 'FUN'.

simplify: logical; should the result be simplified to a vector or
          matrix if possible?

USE.NAMES: logical; if 'TRUE' and if 'X' is character, use 'X' as
          'names' for the result unless it had names already.

       n: number of replications.

    expr: expression to evaluate repeatedly.

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

     Function 'FUN' must be able to accept as input any of the elements
     of 'X'.  If the latter is an atomic vector, 'FUN' will always be
     passed a length-one vector.

     Simplification in 'sapply' is only attempted if 'X' has length
     greater than zero and if the return values from all elements of
     'X' are all of the same (positive) length.  If the common length
     is one the result is a vector, and if greater than one is a matrix
     with a column corresponding to each element of 'X'.

     The mode of the simplified answer is chosen to accommodate the
     modes of all the values returned by the calls to 'FUN': see
     'unlist'.

     if 'X' has length 0, the return value of 'sapply' is always a
     0-length list.

_N_o_t_e:

     'sapply(*, simplify = FALSE, USE.NAMES = FALSE)' is equivalent to
     'lapply(*)'.

_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:

     'apply', 'tapply'.

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

     x <- list(a = 1:10, beta = exp(-3:3), logic = c(TRUE,FALSE,FALSE,TRUE))
     # compute the list mean for each list element
     lapply(x,mean)
     # median and quartiles for each list element
     lapply(x, quantile, probs = 1:3/4)
     sapply(x, quantile)
     i39 <- sapply(3:9, seq) # list of vectors
     sapply(i39, fivenum)

     hist(replicate(100, mean(rexp(10))))

