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

From: Chuck Cleland <ccleland_at_optonline.net>
Date: Sat 25 Feb 2006 - 03:41:55 EST

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.
>

```mydata <- data.frame(
Name = c("ab","ab","ab","ab","dv","dv","dv"),
Year = c(2001,2001,2002,2003,2002,2002,2003),
x = c(15,10,12,7,10,3,1),
y = c(3,2,8,10,15,2,15))

aggregate(mydata[,c("x", "y")],
list(Name = mydata\$Name, Year = mydata\$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

?aggregate

```--
Chuck Cleland, Ph.D.
NDRI, Inc.
71 West 23rd Street, 8th floor
New York, NY 10010
tel: (212) 845-4495 (Tu, Th)
tel: (732) 452-1424 (M, W, F)
fax: (917) 438-0894

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