[R] suggested method to transform list to a matrix

[R. Michael Weylandt]

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
>
>
>
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