[R] Re-assigning vector elements based on their initial values.
Petr Pikal
petr.pikal at precheza.cz
Mon Feb 3 13:05:04 CET 2003
Hi
On 1 Feb 2003 at 7:17, John Fox wrote:
> Dear Rex,
>
> You can use if.else, which is vectorized:
>
> > v.new <- ifelse(v < 0, -v/2, v)
> > v.new
> [1] 5.0 5.0 1.5 1.5 7.0 8.0 10.0
or simply
abs(v/((v<0)+1))
it should be a little bit quicker
>
> (By the way, the solution that you suggested using a loop works, but
> for some reason the sign is wrong in the result that you printed;
> notice that your "else" clause does nothing -- you probably meant to
> assign to v.new not v -- and is unnecessary in any event.)
>
> I hope that this helps,
> John
>
>
>
> At 07:38 PM 1/31/2003 -0700, Rex_Bryan at urscorp.com wrote:
> >Is there an eloquent solution to re-assign vector element values? I
> >have a vector which contains chemical data, some of them are
> >"flagged" as non-detected values by their negative values. I can find
> >the statistics on the positive values in vector "v" simply by
> >typing:
> > >v<- c(5,5,-3,-3,7,8,10)
> >
> > > v[(v>0)]
> >[1] 5 5 7 8 10
> >
> >I can also convert to positive values by
> > >asb(v)
> >[1] 5 5 3 3 7 9 10
> >
> >I then can do mean() and var() etc.
> >
> >But when I want to come up with a way to change a negative value to a
> >postive 1/2 value I couldn't come up with a nice way using "vectoral
> >syntax" to do it. In the method I came up with , I discovered that I
> >have to pre-define a new vector "v.new" or I get an error.
> >
> > >v.new <-v
> >
> >then I have to loop through all of the elements!
> >
> > >for(i in 1:length(v)){ if (v[i] < 0) v.new[i] <- -1*v[i]/2 else
> > >v[i] <-
> >v[i]}
> > > v.new
> >[1] 5.0 5.0 -1.5 -1.5 7.0 9.0 10.0
> >
> >This works but seems labored given the previous crisp vector
> >operations.
>
> -----------------------------------------------------
> John Fox
> Department of Sociology
> McMaster University
> Hamilton, Ontario, Canada L8S 4M4
> email: jfox at mcmaster.ca
> phone: 905-525-9140x23604
> web: www.socsci.mcmaster.ca/jfox
> -----------------------------------------------------
>
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Cheers
Petr
petr.pikal at precheza.cz
p.pik at volny.cz
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