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conditional assignment

5 messages · uaca@alumni.uv.es, Roger Bivand, Simon Cullen +1 more

uaca@alumni.uv.es
# 
Hi all

I want to conditionally operate on certain elements of a matrix, let me
explain it with a simple vector example
[1] 1 2 3

why zz is not (0, 0, 3) ?????


the null <- assignment is to keep the console silent

in the other hand, it curious that null has reasonable values
[1] FALSE FALSE  TRUE

Thanks in advance

	Ulisses

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Roger Bivand
#
On Mon, 26 Jan 2004 uaca at alumni.uv.es wrote:

            

      
      
      
    

        
Break it down into bits:

            

      
      
      
    

        
[1] FALSE FALSE  TRUE

            

      
      
      
    

        
[1] 1 2 3

            

      
      
      
    

        
[1] FALSE FALSE  TRUE

            

      
      
      
    

        
[1] TRUE TRUE TRUE

            

      
      
      
    

        
[1] TRUE TRUE TRUE TRUE
Warning message: 
longer object length
        is not a multiple of shorter object length in: rep(TRUE, 4) & (zz <- z) 

The first part is a logical vector, the second is the result of assigning 
z to zz, & of them isn't terribly meaningful?

Try:

            

      
      
      
    

        
[1] 0 0 3

if that's what you want.

            

      
      
      
    

        

      
      
    

        

  
    

      
      
    

  


  


      

    

    

      
      

        


  

        

      Simon Cullen
    

    

      
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On Mon, 26 Jan 2004 20:15:51 +0100, <uaca at alumni.uv.es> wrote:

        

            

      
      
      
    

        
<snip>

            

      
      
      
    

        
What you have done there is create a boolean vector, null, of the same  
length as z (and zz).

For instance:
(z > 2) & (zz <- z)
=(F F T) & (T T T) (as assignment - presumably - returns T)
=(F F T).

What will work is:
z <- c(1, 2, 3)
index <- z>2
zz <- z * index

  
    

      
      
    

  


  


      

    

    

      
      

        


  

        

      Brian Ripley
    

    

      
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On Mon, 26 Jan 2004, Simon Cullen wrote:

        

            

      
      
      
    

        
assignment returns the new value of zz, which as it is all non-zero
coerces to the logical vector T T T

            

      
      
      
    

        
Rather better I think is

zz <- ifelse(z > 2, z, zz)

or even

ind <- z > 2
zz[ind] <- z[ind]

  
    

      
      
    

  


  


      

    

    
2 days later

    

      
      

        


  

        

      uaca@alumni.uv.es
    

    

      
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Hi all again

I could not reply before because I was/am very busy

ifthenelse() is what I wanted, I have to read more carefully your
explanations to better understand it

Thanks everybody

	Ulisses

        
On Mon, Jan 26, 2004 at 08:15:51PM +0100, uaca at alumni.uv.es wrote: