Hi Andreas,
Try this:
fruit_2sds<-by(data2$molecule,data2$fruit,sd)*2
data2$newcol<-ifelse(data2$molecule>fruit_2sds[data2$fruit],1,0)
or even just:
data$newcol<-as.numeric(data2$molecule>fruit_2sds[data2$fruit])
Jim
On Fri, Oct 14, 2016 at 5:17 PM, Andreas Nord <andreas.n...@biol.lu.se> wrote:
>
> Dear list,
>
> Apologies for a likely naive question.
>
>
> I am trying to create a discriminating dummy variable using 'ifelse' based on
> conditions in two variables.
>
>
> Specifically, I want to assign levels in a new factor as '0' or '1' based on
> a user-defined cut off. I.e. something similar to:
>
> >data1<-data.frame(molecule=runif(30,min=0,max=1e3))
>
>>data1$newcol<-ifelse(data1$molecule>2*sd(data1$molecule),1,0)
>
>
> Which is all straightforward.
>
>
> But how do I go on to assign values in variable 'molecule'based on the same
> cut off, but separately for each level of a second variable, in this case the
> factor 'fruit' with three levels. That is, how do I derive fruit-specific
> cut-offs using a data frame with the general structure of that below?
>
>>data2<-data.frame(molecule=runif(30,min=0,max=1e3),fruit=factor(rep(c('apple','pear','orange'),10)))
>
>
> Many thanks in advance!
>
>
>
> [[alternative HTML version deleted]]
>
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