On 2012-05-15 08:36, Melissa Rosenkranz wrote:
Here is an R problem I am struggling with:
My dataset is organized like this...
subject session variable_x variable_y
01 1 1<interger values>
01 1 2
01 1 3
01 2 1
01 2 2
01 2 3
02 1 1
02 1 2
02 1 3
02 2 1
02 2 2
02 2 3
03 1 1
03 1 2
03 1 3
03 2 1
03 2 2
03 2 3
...
I need to find the level of variable x at which variable y has the maximum
value for each individual for each session. Then, I need to create another
variable, say variable "z" that labels that row in the dataset as the "max"
for that individual at that time. I have searched the archives and the web
for ideas, but am having trouble finding appropriate search terms for what
I need to do. Any advice? Thank you!!
This is one way:
set.seed(123)
d <- data.frame(
subject = gl(3,6,labels=c("01","02","03")),
session = gl(2,3,18),
x = gl(3,1,18),
y = sample(11:15, 18, replace=TRUE))
library(plyr)
ddply(d, .(subject, session), transform,
z = ifelse(y == max(y), 1, 0))
Peter Ehlers
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