[R] Elegant way to transform dataframe?

[ONKELINX, Thierry]

Dear Barry,

Have a look at the function cast() in the reshape package. That should
be able to do what you need.

HTH,

Thierry


------------------------------------------------------------------------
----
ir. Thierry Onkelinx
Instituut voor natuur- en bosonderzoek / Research Institute for Nature
and Forest
Cel biometrie, methodologie en kwaliteitszorg / Section biometrics,
methodology and quality assurance
Gaverstraat 4
9500 Geraardsbergen
Belgium 
tel. + 32 54/436 185
Thierry.Onkelinx op inbo.be 
www.inbo.be 

To call in the statistician after the experiment is done may be no more
than asking him to perform a post-mortem examination: he may be able to
say what the experiment died of.
~ Sir Ronald Aylmer Fisher

The plural of anecdote is not data.
~ Roger Brinner

The combination of some data and an aching desire for an answer does not
ensure that a reasonable answer can be extracted from a given body of
data.
~ John Tukey

-----Oorspronkelijk bericht-----
Van: r-help-bounces op r-project.org [mailto:r-help-bounces op r-project.org]
Namens Barry Rountree
Verzonden: donderdag 20 november 2008 8:39
Aan: r-help op r-project.org
Onderwerp: [R] Elegant way to transform dataframe?

Hello,

I have a dataframe with columns like:

  parameter1 parameter2 metricname value

and I'd like to transform it into a dataframe with columns:

  parameter1 parameter2 metric1 metric2 metric3

where the values for each metric would be in the appropriate column.
There are often multiple values for a given (parameter1, parameter2,
metricname) triple.  In this case, I want to use the minimum value.

A constant number of metrics is associated with each possible
combination of parameters.

I've cobbled together code that performs this using nested loops and far
too many variables.  The number of metrics has now gone up by an order
of magnitude and I'm looking for a more elegant way of doing this.  

If anyone has a short bit of code that can deal with this, I'd really
appreciate having a look.

Thanks much,

Barry

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