R help - Nov 2003 - Find value in vector (or matrix)

Hi all,

Is there a function to check if a particular value is contained in a 
vector? I've looked at grep in the hope that I could use a Perl-like 
syntax, but obviously it's different...

I'd like to do something like:

    y <- c("a","b","c")
    if("a" in y)
    {
          # "a" is not in y
    }

Also, is there a way to generate character sequences similar to numeric 
sequences, e.g. something like "A":"J" ? I remember having
seen a
command doing this somewhere, but can't find it anymore

Thanks

Pascal

On Thu, 20 Nov 2003, Pascal A. Niklaus wrote:
> Is there a function to check if a particular value is contained in a 
> vector? I've looked at grep in the hope that I could use a Perl-like 
> syntax, but obviously it's different...
> 
> I'd like to do something like:
> 
>     y <- c("a","b","c")
>     if("a" in y)
"a" %in" y,

which disguises a call to match(), so look at match.

length(grep("a", y)) > 0 should work too.
>     {
>           # "a" is not in y
>     }
> 
> Also, is there a way to generate character sequences similar to numeric 
> sequences, e.g. something like "A":"J" ? I remember
having seen a
> command doing this somewhere, but can't find it anymore
LETTERS[1:10] will do this.

-- 
Brian D. Ripley,                  ripley at stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
1 South Parks Road,                     +44 1865 272866 (PA)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595

Pascal A. Niklaus wrote:
> Hi all,
> 
> Is there a function to check if a particular value is contained in a 
> vector? I've looked at grep in the hope that I could use a Perl-like 
> syntax, but obviously it's different...
> 
> I'd like to do something like:
> 
>    y <- c("a","b","c")
>    if("a" in y)
>    {
>          # "a" is not in y
>    }
> 
> Also, is there a way to generate character sequences similar to numeric 
> sequences, e.g. something like "A":"J" ? I remember
having seen a
> command doing this somewhere, but can't find it anymore
> 
> Thanks
> 
> Pascal
You almost have it: Try "%in%" instead.

if("a" %in% y) { }

or

if(any(c("a", "b") %in% y)) { }

See help("%in%").

For question 2, see ?letters or ?LETTERS.

-sundar

On Thu, Nov 20, 2003 at 01:26:23PM +0100, Pascal A. Niklaus
wrote:
> Is there a function to check if a particular value is contained in a 
> vector?
> myvec <- c('foo','bar','duh','bonk')
> 'bonk' %in% myvec
[1] TRUE
> 'asdf' %in% myvec
[1] FALSE
> Also, is there a way to generate character sequences similar to numeric 
> sequences, e.g. something like "A":"J" ?
> LETTERS[1:5]
[1] "A" "B" "C" "D" "E"
> letters[c(8,9,12,23)]
[1] "h" "i" "l" "w"

cu
	Philipp

-- 
Dr. Philipp Pagel                                Tel.  +49-89-3187-3675
Institute for Bioinformatics / MIPS              Fax.  +49-89-3187-3585
GSF - National Research Center for Environment and Health
Ingolstaedter Landstrasse 1
85764 Neuherberg, Germany

Pascal A. Niklaus wrote:
>    y <- c("a","b","c")
>    if("a" in y)
>    {
>          # "a" is not in y
>    }
  You are 98% of the way there. The missing two percent is this:

  if("a" %in% y) {
...
}

  you could also use the 'any' function:

  if(any(y=="a")){
...
  }

> Also, is there a way to generate character sequences similar to numeric 
> sequences, e.g. something like "A":"J" ? I remember
having seen a
> command doing this somewhere, but can't find it anymore
  R defines two vectors, "letters" and "LETTERS" which have
the 26 lower
and upper-case letters of the English alphabet. Subset from them to get 
what you want.

Baz

"Pascal A. Niklaus" <Pascal.Niklaus at unibas.ch> writes:
> Hi all,
> 
> Is there a function to check if a particular value is contained in a
> vector? I've looked at grep in the hope that I could use a Perl-like
> syntax, but obviously it's different...
> 
> I'd like to do something like:
> 
>     y <- c("a","b","c")
>     if("a" in y)
>     {
>           # "a" is not in y
>     }
"a" %in% y
> Also, is there a way to generate character sequences similar to
> numeric sequences, e.g. something like "A":"J" ? I
remember having
> seen a command doing this somewhere, but can't find it anymore
LETTERS[1:10] 

is probably the closest. You do need to look up that "J" is the 10th
letter or resort to things like

LETTERS[which(LETTERS>="A"&LETTERS<="J")]

or

LETTERS[which(LETTERS=="A"):which(LETTERS=="J")]


-- 
   O__  ---- Peter Dalgaard             Blegdamsvej 3  
  c/ /'_ --- Dept. of Biostatistics     2200 Cph. N   
 (*) \(*) -- University of Copenhagen   Denmark      Ph: (+45) 35327918
~~~~~~~~~~ - (p.dalgaard at biostat.ku.dk)             FAX: (+45) 35327907