Re: [R] Summarize by two-column factor, retaining original factors

From: Marc Schwartz (via MN) <mschwartz_at_mn.rr.com>
Date: Sat 25 Feb 2006 - 03:29:11 EST

On Fri, 2006-02-24 at 08:18 -0800, Matt Crawford wrote:
> I am having trouble doing the following. I have a data.frame like
> this, where x and y are a variable that I want to do calculations on:
>
> Name Year x y
> ab 2001 15 3
> ab 2001 10 2
> ab 2002 12 8
> ab 2003 7 10
> dv 2002 10 15
> dv 2002 3 2
> dv 2003 1 15
>
> Before I do all the other things I need to do with this data, I need
> to summarize or collapse the data by name and year. I've found that I
> can do things like
> nameyear<-interaction(name,year)
> dataframe$nameyear<-nameyear
> tapply(dataframe$x,dataframe$nameyear,sum)
> tapply(dataframe$y,dataframe$nameyear,sum)
> and then bind those together.
>
> But my problem is that I need to somehow retain the original Names in
> my collapsed dataset, so that later I can do analyses with the Name
> factors. All I can think of is something like
> tapply(dataframe$Name,dataframe$nameyear, somefunction?)
> but nothing seems to work.
>
> I'm actually trying to convert a SAS program, and I can't get out of
> that mindset. There, it's a simple Proc Means, By Name Year.
>
> Thanks for any help or suggestions on the right way to go about this.
>
> Matt Crawford

Matt,

Just use aggregate():

> aggregate(MyDF[, 3:4], list(Name = MyDF$Name, Year = MyDF$Year), sum)
  Name Year x y
1 ab 2001 25 5
2 ab 2002 12 8
3 dv 2002 13 17
4 ab 2003 7 10
5 dv 2003 1 15

See ?aggregate for more information.

HTH, Marc Schwartz



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