max value
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