[R] programming question

Peter Dalgaard BSA p.dalgaard at biostat.ku.dk
Thu Nov 8 22:40:46 CET 2001

Clayton Springer <csprin at brandybuck.ca.sandia.gov> writes:

> Dear r-help,
> I am trying to build a new function (to process rpart objects) that will
> output matrix that has a row for each node and a column for
> each feature. With each entry in the table is a numerical property
> at that node for that feature (e.g. surrogate split agreement, improvement).
> My current trouble is that the only clue to the identity of the feature is 
> stored as the *name* of the feature.  Whereas a table is indexed by *number*.
> I have a list of sorted names, but I am having trouble translating a name
> into a number. If this where perl the answer would be a hash.
> Or can I directly index a table with an alphanumeric string. (ie. a hash).
> Any help would be greatly appreciated,

You can easily index with names:

> x<-1:3
> names(x)<-letters[1:3]
> x
a b c 
1 2 3 
> x["b"]

It's not a hash in the perl sense, though. Each lookup does a linear
search. The match() function could also be used.

   O__  ---- Peter Dalgaard             Blegdamsvej 3  
  c/ /'_ --- Dept. of Biostatistics     2200 Cph. N   
 (*) \(*) -- University of Copenhagen   Denmark      Ph: (+45) 35327918
~~~~~~~~~~ - (p.dalgaard at biostat.ku.dk)             FAX: (+45) 35327907
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