[R] Elegant way to transform dataframe?
rountree at uga.edu
Sun Nov 23 19:00:15 CET 2008
---- Original message ----
>Date: Thu, 20 Nov 2008 09:41:11 +0100
>From: "David Hajage" <dhajage.r at gmail.com>
>Subject: Re: [R] Elegant way to transform dataframe?
>To: "Barry Rountree" <rountree at uga.edu>
> I suggest you to have a look to the reshape package,
> by Hadley Wickham : http://had.co.nz/reshape/
That's exactly what I needed -- thanks!
A few comments for other people who might be interested in trying it:
1) "reshape" is the name of the package, "melt" and "cast" are the commands. There's a "reshape" command that's part of the stats package and it does something similar, but it's not nearly so general.
2) I didn't find the package documentation helpful, but the website has links to several papers that provide much better examples.
3) The package requires an up-to-date version of R. I had been using an old version and trying to install the package gave a "not found" error. It wasn't until I downloaded the package and tried a local install that I got a useful error message about the version mismatch.
> 2008/11/20 Barry Rountree <rountree at uga.edu>
> I have a dataframe with columns like:
> parameter1 parameter2 metricname value
> and I'd like to transform it into a dataframe with
> 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,
> R-help at r-project.org mailing list
> PLEASE do read the posting guide
> and provide commented, minimal, self-contained,
> reproducible code.
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