Thank you Phil. The only problem with the code is when the 2 y values are
equal,
it should default to "right". Your code would default to the first maximum. But
it's ok, I see the logic here and can figure it out. I wondered whether there
is
some one-line thing that can do this, I guess not possible.
Thank you
John
________________________________
From: Phil Spector <spec...@stat.berkeley.edu>
Cc: r-help@r-project.org
Sent: Fri, October 1, 2010 10:58:55 AM
Subject: Re: [R] add a new column to data frame
Here are two ways:
dat0 = subset(dat,time==0)
one = as.data.frame(as.table(by(dat0,dat0$id,
function(x)as.character(x$mode)[which.max(x$y)])))
names(one) = c('id','type')
merge(dat,one)
two = sapply(split(dat0,dat0$id),
function(x)as.character(x$mode)[which.max(x$y)])
merge(dat,data.frame(id=names(two),type=two))
- Phil Spector
Statistical Computing Facility
Department of Statistics
UC Berkeley
spec...@stat.berkeley.edu
On Fri, 1 Oct 2010, array chip wrote:
> Hi, I am wondering if anyone can propose a simple/best way to do the
following:
>
> Let's say I have a data frame
>
> dat <-
>cbind(expand.grid(mode=c('right','left'),time=0:3,id=c('p1','p2','p3')),y=c(3,5,rep(4,6),6,2,rep(3,6),4,4,rep(2,6)))
>)
>
>
> dat
> mode time id y
> 1 right 0 p1 3
> 2 left 0 p1 5
> 3 right 1 p1 4
> 4 left 1 p1 4
> 5 right 2 p1 4
> 6 left 2 p1 4
> 7 right 0 p2 6
> 8 left 0 p2 2
> 9 right 1 p2 3
> 10 left 1 p2 3
> 11 right 2 p2 3
> 12 left 2 p2 3
> 13 right 0 p3 4
> 14 left 0 p3 4
> 15 right 1 p3 2
> 16 left 1 p3 2
> 17 right 2 p3 2
> 18 left 2 p3 2
>
> Now I want to add a new column "type" to this data frame with values of either
> "left" or "right" for each "id" based on the following logic:
>
> For each "id", the value of "type" column is the value of "mode" for which the
> value of "y" is the maximum of "y" based on time=0. For example for id=p1, the
> value of "type" is "left" because for the 2 "y" values (3 & 5) based on
time=0,
> mode=left has the bigger "y" value (5). But if the 2 "y" values are the same
>for
> "mode", then let type=right.
>
> In the end the new data frame is:
>
> mode time id y type
> 1 right 0 p1 3 left
> 2 left 0 p1 5 left
> 3 right 1 p1 4 left
> 4 left 1 p1 4 left
> 5 right 2 p1 4 left
> 6 left 2 p1 4 left
> 7 right 0 p2 6 right
> 8 left 0 p2 2 right
> 9 right 1 p2 3 right
> 10 left 1 p2 3 right
> 11 right 2 p2 3 right
> 12 left 2 p2 3 right
> 13 right 0 p3 4 right
> 14 left 0 p3 4 right
> 15 right 1 p3 2 right
> 16 left 1 p3 2 right
> 17 right 2 p3 2 right
> 18 left 2 p3 2 right
>
> Any suggestions would be appreciated.
>
> John
>
>
>
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>
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