> i am looking from some insights to define own R functions. so far i
> found most basics in documentations that are around on the web. except
> for one thing:
>
> I´d like to define some function, say:
>
> #assume my data matrix contains vectors like data$myColumn1,data
> $myColumn2 etc.
Do you really mean data matrix, or do you mean data frame?
> getMyColumn <- function (columnid){
>
> x<-data$MyColumn?columnid?[data$indexone=1 & data$index2=5]
>
> return(x)
>
> }
It's not terribly clear what you want to do with this function. Question
marks don't mean anything in the middle of a statement, so I don't know
what
data$MyColumn?columnid?[data$indexone=1 & data$index2=5]
is supposed to do.
Also, you don't need the return keyword - the last line of a function is
the return value.
> Do I need to use assign or eval first ? I tried to use paste to
> combine something like: paste("data$MyColumn",columnid,sep="") which
> did not work.
paste returns a string, not a variable. You can evaluate the contents of
the string using
eval(parse(text=paste("data$MyColumn",columnid,sep="")))
This is however a method of last resort; there is almost always a better
way to do things than using eval.
> I am happy to get any help with the problem, but also thankful for
> some useful link or guide on how to define own functions properly,
> especially the dynamic naming and return part
You probably don't need to bother with dynamic naming, but take a look at
FAW on R, q7.21.
Regards,
Richie.
Mathematical Sciences Unit
HSL
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