R help - Mar 2003 - how to find the location of the first TRUE of a logical vector

without having to check the vector element by element? Thanks a lot!

Jason

====Jason G. Liao, Ph.D.
Division of Biometrics
University of Medicine and Dentistry of New Jersey
335 George Street, Suite 2200
New Brunswick, NJ 08903-2688
phone (732) 235-8611, fax (732) 235-9777
http://www.geocities.com/jg_liao

>-----Original Message-----
>From: r-help-bounces at stat.math.ethz.ch 
>[mailto:r-help-bounces at stat.math.ethz.ch] On Behalf Of Jason Liao
>Sent: Wednesday, March 05, 2003 3:36 PM
>To: r-help at stat.math.ethz.ch
>Subject: [R] how to find the location of the first TRUE of a 
>logical vector
>
>
>without having to check the vector element by element? Thanks a lot!
>
>Jason
>
>====>Jason G. Liao, Ph.D.
>Division of Biometrics
>University of Medicine and Dentistry of New Jersey
>335 George Street, Suite 2200
>New Brunswick, NJ 08903-2688
>phone (732) 235-8611, fax (732) 235-9777 
>http://www.geocities.com/jg_liao

If 'lv' if your logical vector, you could use something like:

min(which(lv == TRUE))

which() would return a vector of the indices within 'lv' that match
TRUE and of course min() will give you the lowest index value.

An example:
> lv <- c(FALSE, FALSE, FALSE, TRUE, TRUE, FALSE, TRUE)
> lv
[1] FALSE FALSE FALSE  TRUE  TRUE FALSE  TRUE
> min(which(lv == TRUE))
[1] 4


HTH,

Marc Schwartz

Jason Liao <jg_liao at yahoo.com> writes:
> without having to check the vector element by element? Thanks a lot!
If vec is your vector of logical values then

match(TRUE, vec)

should work.  It will return NA if there are no TRUE values.

It might not be the most elegant, but it works:
> foo <- c(F, F, T, F, T, T, F ,T)
> c(1:length(foo))[foo][1]
[1] 3
>
And if there is no 'T', it returns 'NA'
> foo <- c(F, F)
> c(1:length(foo))[foo][1]
[1] NA

Martina

--------------------------------------------------------------------------
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1958 Neil Avenue, 304E Cockins Hall  FAX: (614) 292-2096
The Ohio State University            E-mail: pavlicov at stat.ohio-state.edu
Columbus, OH 43210-1247              www.stat.ohio-state.edu/~pavlicov


On Wed, 5 Mar 2003, Jason Liao wrote:
> without having to check the vector element by element? Thanks a lot!
>
> Jason
>
> ====> Jason G. Liao, Ph.D.
> Division of Biometrics
> University of Medicine and Dentistry of New Jersey
> 335 George Street, Suite 2200
> New Brunswick, NJ 08903-2688
> phone (732) 235-8611, fax (732) 235-9777
> http://www.geocities.com/jg_liao
>
> ______________________________________________
> R-help at stat.math.ethz.ch mailing list
> https://www.stat.math.ethz.ch/mailman/listinfo/r-help
>

Try,

x <- c(F,F,F,T,F,T,F,T)
min(which(x))

-roger
_______________________________
UCLA Department of Statistics
rpeng at stat.ucla.edu
http://www.stat.ucla.edu/~rpeng

On Wed, 5 Mar 2003, Jason Liao wrote:
> without having to check the vector element by element? Thanks a lot!
> 
> Jason
> 
> ====> Jason G. Liao, Ph.D.
> Division of Biometrics
> University of Medicine and Dentistry of New Jersey
> 335 George Street, Suite 2200
> New Brunswick, NJ 08903-2688
> phone (732) 235-8611, fax (732) 235-9777
> http://www.geocities.com/jg_liao
> 
> ______________________________________________
> R-help at stat.math.ethz.ch mailing list
> https://www.stat.math.ethz.ch/mailman/listinfo/r-help
>

> >
> >without having to check the vector element by element? Thanks a lot!
which.max() will coerce the logical to numeric and give the location of
the first max, which is the first TRUE.

J.R. Lockwood
412-683-2300 x4941
lockwood at rand.org
http://www.rand.org/methodology/stat/members/lockwood/

Many thanks to all who replied: Marc Schwartz, Douglas Grove, Spencer
Graves, J.R. Lockwood, Roger Peng, Martina Pavlicova, Steve
Su,james.holtman, Wiener, Matthew, Domijan, Katarina and Douglas Bates.
 

Let x be the logical vector. The best solution seems to be: 
which(x)[1].

Now my code is much simpler.

Jason 


====Jason G. Liao, Ph.D.
Division of Biometrics
University of Medicine and Dentistry of New Jersey
335 George Street, Suite 2200
New Brunswick, NJ 08903-2688
phone (732) 235-8611, fax (732) 235-9777
http://www.geocities.com/jg_liao

Many thanks to all who replied: Marc Schwartz, Douglas Grove, Spencer
Graves, J.R. Lockwood, Roger Peng, Martina Pavlicova, Steve
Su,james.holtman, Wiener, Matthew, Domijan, Katarina and Douglas Bates.
 

Let x be the logical vector. The best solution seems to be: 
which(x)[1].

Now my code is much simpler.

Jason 


====Jason G. Liao, Ph.D.
Division of Biometrics
University of Medicine and Dentistry of New Jersey
335 George Street, Suite 2200
New Brunswick, NJ 08903-2688
phone (732) 235-8611, fax (732) 235-9777
http://www.geocities.com/jg_liao

Many thanks to all who replied: Marc Schwartz, Douglas Grove, Spencer
Graves, J.R. Lockwood, Roger Peng, Martina Pavlicova, Steve
Su,james.holtman, Wiener, Matthew, Domijan, Katarina and Douglas Bates.
 

Let x be the logical vector. The best solution seems to be: 
which(x)[1].

Now my code is much simpler.

Jason 


====Jason G. Liao, Ph.D.
Division of Biometrics
University of Medicine and Dentistry of New Jersey
335 George Street, Suite 2200
New Brunswick, NJ 08903-2688
phone (732) 235-8611, fax (732) 235-9777
http://www.geocities.com/jg_liao