is.finite                package:base                R Documentation

_F_i_n_i_t_e, _I_n_f_i_n_i_t_e _a_n_d _N_a_N _N_u_m_b_e_r_s

_D_e_s_c_r_i_p_t_i_o_n:

     `is.finite' and `is.infinite' return a vector of the same length
     as `x', indicating which elements are finite or not.

     `Inf' and `-Inf' are positive and negative `infinity' whereas
     `NaN' means ``Not a Number''.

_U_s_a_g_e:

     is.finite(x)
     is.infinite(x)
     Inf
     NaN
     is.nan(x)

_D_e_t_a_i_l_s:

     `is.finite' returns a vector of the same length as `x' the jth
     element of which is `TRUE' if `x[j]' is finite (i.e. it is not one
     of the values `NA', `NaN', `Inf' or `-Inf').

     `is.infinite' returns a vector of the same length as `x' the jth
     element of which is `TRUE' if `x[j]' is infinite (i.e. equal to
     one of `Inf' or `-Inf').

_N_o_t_e:

     In R, basically all mathematical functions (including basic
     `Arithmetic'), are supposed to work properly with `+/- Inf' and
     `NaN' as input or output.

     The basic rule should be that calls and relations with `Inf's
     really are statements with a proper mathematical limit, see the
     many examples below.

_R_e_f_e_r_e_n_c_e_s:

     ANSI/IEEE 754 Floating-Point Standard.

     Currently (6/1999), Bill M.'s billm@melbpc.org.au tutorial and
     examples at 
     <URL: http://www.linuxsupportline.com/~billm/>

_S_e_e _A_l_s_o:

     `NA', `Not Available' which is not a number as well, however
     usually used for missing values.

_E_x_a_m_p_l_e_s:

     pi / 0 ## = Inf a non-zero number divided by zero creates infinity
     0 / 0  ## =  NaN

     1/0 + 1/0# Inf
     1/0 - 1/0# NaN

     stopifnot(
         1/0 == Inf,
         1/Inf == 0
     )
     exp(-Inf) == 0
     ##              (actually, the last one seems to give NA on not-very-new
     ##               versions of Linux, which is a Linux bug and seems to be
     ##               corrected in newer 'libc6' based Linuxen).

     stopifnot(
         is.na(0/0),
         !is.na(Inf),
         is.nan(0/0),

         !is.nan(NA)  &&  !is.infinite(NA)  && !is.finite(NA),
          is.nan(NaN) &&  !is.infinite(NaN) && !is.finite(NaN),
         !is.nan(c(1,NA)),
         c(F,T,F) == is.nan(c   (1,NaN,NA)),
         c(F,T,F) == is.nan(list(1,NaN,NA))#-> FALSE in older versions
     )


     lgamma(Inf) == Inf
     Inf + Inf == Inf
     Inf - Inf == NaN # NA --- should test with  'is.nan()

     (1/0) * (1/0)# Inf
     (1/0) / (1/0)# NaN

     pm <- c(-1,1) # 'pm' = plus/minus

     log(0) == - 1/0
     exp(-Inf) == 0

     sin(Inf)
     cos(Inf)
     tan(Inf)
     all(atan(Inf*pm) == pm*pi/2) # TRUE

     x <- c(100,-1e-13,Inf,-Inf, NaN, pi, NA)
     x #  1.000000 -3.000000       Inf      -Inf        NA  3.141593        NA
     names(x) <- formatC(x, dig=3)
     is.finite(x)
     ##-   100 -1e-13 Inf -Inf NaN 3.14 NA
     ##-     T      T   .    .   .    T  .
     is.na(x)
     ##-   100 -1e-13 Inf -Inf NaN 3.14 NA
     ##-     .      .   .    .   T    .  T
     which(is.na(x) & !is.nan(x))# only 'NA': 7

     is.na(x) | is.finite(x)
     ##-   100 -1e-13 Inf -Inf NaN 3.14 NA
     ##-     T      T   .    .   T    T  T
     is.infinite(x)
     ##-   100 -1e-13 Inf -Inf NaN 3.14 NA
     ##-     .      .   T    T   .    .  .

     ##-- either  finite or infinite  or  NA:
     all(is.na(x) != is.finite(x) | is.infinite(x)) # TRUE
     all(is.nan(x) != is.finite(x) | is.infinite(x)) # FALSE: have 'real' NA

     ##--- Integer
     (ix <- structure(as.integer(x),names= names(x)))
     ##-   100 -1e-13        Inf        -Inf NaN 3.14 NA
     ##-   100      . 2147483647 -2147483648  NA    3 NA
     all(is.na(ix) != is.finite(ix) | is.infinite(ix)) # TRUE (still)

     ix[3] == (iI <- as.integer(Inf))#> warning: inaccurate integer conversion!
     ix[4] == (imI<- as.integer(-Inf))
     iI  == .Machine$integer.max # TRUE
     imI == -.Machine$integer.max # TRUE

     ##--- Overflow in simple integer arithmetic:
     as.integer(2)*iI #  -2
     as.integer(3)*iI #  2147483645
     as.integer(3)*iI == iI-2 # TRUE

     storage.mode(ii <- -3:5)
     storage.mode(zm <- outer(ii,ii, FUN="*"))# integer
     storage.mode(zd <- outer(ii,ii, FUN="/"))# double
     range(zd, na.rm=T)# -Inf  Inf
     zd[,ii==0]

     (storage.mode(print(1:1 / 0:0)))# Inf "double"
     (storage.mode(print(1:1 / 1:1)))# 1 "double"
     (storage.mode(print(1:1 + 1:1)))# 2 "integer"
     (storage.mode(print(2:2 * 2:2)))# 4 "integer"

