R help - Apr 2012 - suggested method to transform list to a matrix

I have data in the following list format:

USER,VARIABLE,COUNT
user1, var1, 3
user1, var2, 4
user2, var1, 7
userN, var12, 5

And would like to have it format as a matrix: 

		var1		var2		var12
user1	3		4
user2	7
userN					5

What is the suggested method to do this for 1 million rows, with 12 variables
and ~ 4,000 unique users?

Thank you,

Tim Stutt
tim@ischool.berkeley.edu



	[[alternative HTML version deleted]]

Use matrix subsetting like this:

x <- matrix(1:9,3)
rownames(x) <- letters[1:3]
colnames(x) <- LETTERS[1:3]

print(x)

usrs <- c("a","b","a")
vars <- c("C","C","A")
counts <- c(10,11,12)

x[cbind(usrs, vars)] <- counts

print(x)

Hope this helps,
Michael

On Thu, Apr 19, 2012 at 1:48 PM, Tim Stutt <tim at ischool.berkeley.edu>
wrote:
> I have data in the following list format:
>
> USER,VARIABLE,COUNT
> user1, var1, 3
> user1, var2, 4
> user2, var1, 7
> userN, var12, 5
>
> And would like to have it format as a matrix:
>
> ? ? ? ? ? ? ? ?var1 ? ? ? ? ? ?var2 ? ? ? ? ? ?var12
> user1 ? 3 ? ? ? ? ? ? ? 4
> user2 ? 7
> userN ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? 5
>
> What is the suggested method to do this for 1 million rows, with 12
variables and ~ 4,000 unique users?
>
> Thank you,
>
> Tim Stutt
> tim at ischool.berkeley.edu
>
>
>
> ? ? ? ?[[alternative HTML version deleted]]
>
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.

On Apr 19, 2012, at 1:48 PM, Tim Stutt wrote:
> I have data in the following list format:
>
> USER,VARIABLE,COUNT
> user1, var1, 3
> user1, var2, 4
> user2, var1, 7
> userN, var12, 5
>
> And would like to have it format as a matrix:
>
> 		var1		var2		var12
> user1	3		4
> user2	7
> userN					5
>
> What is the suggested method to do this for 1 million rows, with 12  
> variables and ~ 4,000 unique users?
?xtabs

xtabs( COUNT ~ USER + VARIABLE, data=dfrm )

-- 

David Winsemius, MD
West Hartford, CT