Re: 'Condition' statment

[Tony Plate <tplate@acm.org>]

'if' is not intended to accept vectors in the condition.  When given
a vector, it uses only the first element to decide whether to execute the
if or else block, and prints a warning to that effect:

> if (c(F)) T else F
[1] F
> if (c(T)) T else F
[1] T
> if (c(T,T)) T else F
Warning: Condition has 2 elements: only the first used: if(c(T, T)) T
else F
[1] T
> if (c(T,F)) T else F
Warning: Condition has 2 elements: only the first used: if(c(T, F)) T
else F
[1] T
> if (c(F,T)) T else F
Warning: Condition has 2 elements: only the first used: if(c(F, T)) T
else F
[1] F
> 

hope this helps,

Tony Plate


At Friday 04:08 PM 1/9/2004 -0500, Lambert.Winnie wrote:
> All,
>  
> S-PLUS 6.0 R2, Windows XP
>  
> I have a scritp with nested IF algorithm in a
> WHILE loop:
>  
> ...
> iter <- iter+1
> if (iter > 25)
> {
>     if ( abs(wsold[good] -
> wsnew[good] ) < wstol/10 )
>     {
>        
> goodc <- abs(wsnew[good] - w[good]) <
> 10*wstol
>        
> tlcl[good][!goodc] <- NA
>        
> plcl[good[!goodc} <- NA
>         brk
> <- 1
>     }
>     else
>     {
>        
> tlcl[good] <- NA
>        
> plcl[good] <- NA
>         brk
> == 1
>     }
> }
> if (brk == 1) break
> ...
>  
> Basically, if the specified condition in the
> while loop is not met after 25 iterations, the inner IF algorithm is
> invoked.  wsold, wsnew, w, tlcl, and plcl are vectors of the same
> length.  In one particular case where the vectors have a length of
> 92, 7 elements have not met the criteria necessary to end the WHILE loop
> and the nested IF statement is invoked.  Upon completion, I get the
> message
>  
> Condition has 7 elements: only the first used
> in: if(abs(wsold[good] - wsnew[good]) < wstol/10) { ....
>  
> Would someone mind telling me what this
> means?  A manual inspection revealed that all of the 7 elements met
> the condition in the nested IF statement and it appears that the commands
> under the IF statement were executed.  Thanks for any info you can
> provide.
>  
> Win Lambert
>
> **********************************************
> Winifred C. Lambert   Senior Scientist/Meteorologist
> ENSCO, Inc.
> Aerospace Sciences and Engineering Division
> 1980 N. Atlantic Ave., Suite 230
> Cocoa Beach, FL  32931
> VOICE: 321.853.8130  FAX: 321.853.8415
> EMAIL: lambert.winifred@ensco.com
>
> AMU Quarterly Reports are available online:
> http://science.ksc.nasa.gov/amu/home.html
> ******************************************** 
>

Tony Plate   tplate@acm.org