Hello all,
An elementary question that I am sure can be easily cracked by an R
enthusiast. Let's say I have multiple scores (y) on subjects (x.sample).
Some subjects have a few more scores than others. Can somebody suggest some
code that will select the first score for each subject?
For example, the following code generates scores for 5 subjects:
> x <- c(1:5)
> x.sample <- sample(x, 20, replace = TRUE)
> x.sample <- sort(x.sample)
> y <- rnorm(20)
> z <- cbind(x.sample, y)
> z
x.sample y
[1,] 1 -1.2006469
[2,] 1 0.7615261
[3,] 1 -0.1287516
[4,] 1 - 1.1796474
[5,] 1 -1.2902519
[6,] 2 -0.1614918
[7,] 2 -0.1464773
[8,] 2 -0.8875417
[9,] 2 0.3062891
[10,] 2 0.4398530
[11,] 3 -0.5717729
[12,] 3 - 0.2938118
[13,] 4 -0.2398887
[14,] 4 0.8425419
[15,] 4 2.5269801
[16,] 4 -0.3643613
[17,] 5 1.1690564
[18,] 5 -0.7644521
[19,] 5 1.4178982
[20,] 5 - 0.8198921
I am only interested in extracting the first score (y) for each unique
subject (x.sample). So, I would like to generate the following output.
x.sample y
[1,] 1 -1.2006469
[2,] 2 -0.1614918
[3,] 3 -0.5717729
[4,] 4 -0.2398887
[5,] 5 1.1690564
Any assistance would be greatly appreciated.
Regards,
Brian
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