Is this what you want:
> test.data
x group
1 32.66782 A
2 50.02132 A
3 43.69700 A
4 46.59031 A
5 38.43428 A
6 68.03142 A
7 46.68868 A
8 33.94487 A
9 51.97193 A
10 52.63176 A
11 40.14173 B
12 21.11079 B
13 43.59518 B
14 55.70508 B
15 49.40277 B
16 49.01821 B
17 55.60821 B
18 38.13541 B
19 60.96777 B
20 49.94656 B
> test.data$z <- ave(test.data$x,
> test.data$group,FUN=function(z){(z-mean(z))/sd(z)})
> test.data
x group z
1 32.66782 A -1.33241490
2 50.02132 A 0.34308231
3 43.69700 A -0.26753700
4 46.59031 A 0.01181557
5 38.43428 A -0.77565765
6 68.03142 A 2.08197466
7 46.68868 A 0.02131284
8 33.94487 A -1.20911451
9 51.97193 A 0.53141612
10 52.63176 A 0.59512257
11 40.14173 B -0.54637780
12 21.11079 B -2.21770874
13 43.59518 B -0.24308968
14 55.70508 B 0.82042267
15 49.40277 B 0.26694269
16 49.01821 B 0.23317041
17 55.60821 B 0.81191546
18 38.13541 B -0.72257633
19 60.96777 B 1.28260182
20 49.94656 B 0.31469951
>
On 9/27/07, [EMAIL PROTECTED] <[EMAIL PROTECTED]> wrote:
>
> tapply is also very useful:
>
>
> my.df<-data.frame(x=rnorm(20, 50, 10),group=factor(sort(rep(c("A", "B"),
> 10))))
> tapply(my.df$x,my.df$group,function(x){(x-mean(x))/sd(x)})
>
>
>
> -----Original Message-----
> From: [EMAIL PROTECTED]
> [mailto:[EMAIL PROTECTED] Behalf Of Matthew Dubins
> Sent: 26 September 2007 21:57
> To: r-help@r-project.org
> Subject: [R] Getting group-wise standard scores of a vector
>
>
> Hi,
>
> I want to be able to create a vector of z-scores from a vector of
> continuous data, conditional on a group membership vector.
>
> Say you have 20 numbers distributed normally with a mean of 50 and an sd
> of 10:
>
> x <- rnorm(20, 50, 10)
>
>
> Then you have a vector that delineates 2 groups within x:
>
> group <- sort(rep(c("A", "B"), 10))
>
> test.data <- data.frame(cbind(x, group))
>
> I know that if you break up the x vector into 2 different vectors then
> it becomes easy to calculate the z scores for each vector, then you
> stack them and append them to the original
> data frame. Is there anyway to apply this sort of calculation without
> splitting the original vector up? I tried a really complex ifelse
> statement but it didn't seem to work.
>
> Thanks in advance,
> Matthew Dubins
>
> ______________________________________________
> R-help@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.
>
> ______________________________________________
> R-help@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.
>
--
Jim Holtman
Cincinnati, OH
+1 513 646 9390
What is the problem you are trying to solve?
______________________________________________
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and provide commented, minimal, self-contained, reproducible code.
