Logic                  package:base                  R Documentation

_L_o_g_i_c_a_l _O_p_e_r_a_t_o_r_s

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

     These operators act on logical vectors.

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

     ! x
     x & y
     x && y
     x | y
     x || y
     xor(x, y)

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

    x, y: logical vectors

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

     '!' indicates logical negation (NOT).

     '&' and '&&' indicate logical AND and '|' and '||' indicate
     logical OR.  The shorter form performs elementwise comparisons in
     much the same way as arithmetic operators.  The longer form
     evaluates left to right examining only the first element of each
     vector.  Evaluation proceeds only until the result is determined. 
     The longer form is appropriate for programming control-flow and
     typically preferred in 'if' clauses.

     'xor' indicates elementwise exclusive OR.

     'NA' is a valid logical object.  Where a component of 'x' or 'y'
     is 'NA', the result will be 'NA' if the outcome is ambiguous.  In
     other words 'NA & TRUE' evaluates to 'NA', but 'NA & FALSE'
     evaluates to 'FALSE'.  See the examples below.

_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:

     'TRUE' or 'logical'.

     'Syntax' for operator precedence.

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

     y <- 1 + (x <- rpois(50, lambda=1.5) / 4 - 1)
     x[(x > 0) & (x < 1)]    # all x values between 0 and 1
     if (any(x == 0) || any(y == 0)) "zero encountered"

     ## construct truth tables :

     x <- c(NA, FALSE, TRUE)
     names(x) <- as.character(x)
     outer(x, x, "&")## AND table
     outer(x, x, "|")## OR  table

