[R] vectorizing test for equality

[Eric Lecoutre]

Take a look at 'any', which allows to remove missing values before test:

any(y==3, na.rm=TRUE)

If your vector does not contain integers, dont forget to change 'y==3' test 
by something more appropriate. (begin to round with a fixed number of dec. 
for exemple).

Eric

At 00:15 20/12/2002 -0800, you wrote:
>Dear R Help,
>    I am trying to create a boolean vector that is TRUE whenever a
>particular value occurs in a numeric vector, and FALSE otherwise.  For
>example, suppose that
>
> > y <- c(5, 2, 4, 3, 1)
> > y
>[1] 5 2 4 3 1
>
>and suppose that I want to find where 3 occurs in y.  Then, the following
>yields the solution:
>
> > y == 3
>[1] FALSE FALSE FALSE  TRUE FALSE
>
>My problem arises when the numeric vector has missing values.  For
>example, suppose that x is the vector
>
> > x <- c( 2, NA, 1, 5, 3)
> > x
>[1]  2 NA  1  5  3
>
>Now x == 5 yields
>
> > x == 5
>[1] FALSE    NA FALSE  TRUE FALSE
>
>whereas what I want is
>
>FALSE  FALSE  FALSE  TRUE  FALSE
>
>I can solve this problem with a for loop:
>
> > flag <- NULL
> > for (i in 1:length(x)) flag <- c(flag, identical(x[i], 5))
> > flag
>[1] FALSE FALSE FALSE  TRUE FALSE
>
>Is there a way to avoid the for loop?  I'm also curious why the following
>does not work, because it seems to me it should:
>
> > test <- function(x) identical(x[1], x[2])
> > apply(cbind(x, 5), 1, test)
>[1] FALSE FALSE FALSE FALSE FALSE
>
>I was expecting to see FALSE FALSE FALSE TRUE FALSE.
>
>John Miyamoto
>
>--------------------------------------------------------------------
>John Miyamoto, Dept. of Psychology, Box 351525
>University of Washington, Seattle, WA 98195-1525
>Phone 206-543-0805, Fax 206-685-3157, Email jmiyamot at u.washington.edu
>Homepage http://faculty.washington.edu/jmiyamot/
>--------------------------------------------------------------------
>
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__________________________________________________

Eric Lecoutre           Informaticien/Statisticien
Institut de Statistique                        UCL

                               (+32) (0)10 47 30 50
                            lecoutre at stat.ucl.ac.be
     http://www.stat.ucl.ac.be/ISpersonnel/lecoutre
__________________________________________________
Le vrai danger, ce n'est pas quand les ordinateurs
penseront comme des hommes, c'est quand les hommes
penseront comme des ordinateurs.     Sydney Harris