Message-ID: <4FB28430.5060406@ucalgary.ca>
Date: 2012-05-15T16:28:32Z
From: Peter Ehlers
Subject: max value
In-Reply-To: <CAB6-=dTf5J3a+X1b+FfKPpzbwM=BJQ-teV=FHWMQyfN4H4dpeA@mail.gmail.com>
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