R help - Apr 2013 - Using PLYR to apply a custom function to a data frame

Hello,

I am still struggling w/ the PLYR syntax.  I am trying to build a customized
function to detect outliers in a data frame based on the interquantile
method.  My data frame is called "ALL" &  I am trying to create
two new
variables in my data frame:
upper=q3+ 1.5*(q3-q1)   & lower=q1-1.5*(q3-q1).  I already have variables q1
& q3.  How could I create the upper and lower variables using plyr so that
it applies to the whole dataframe.  Thank you for your help.



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Hi,
You could try ?within()
set.seed(25)
ALL<- data.frame(q3=sample(15:30,10,replace=TRUE),
q1=sample(1:14,10,replace=TRUE))


res<-within(ALL,{lower<-q1- 1.5*(q3-q1);upper<-q3+1.5*(q3-q1)})
?res
#?? q3 q1 upper lower
#1? 21? 5? 45.0 -19.0
#2? 26? 6? 56.0 -24.0
#3? 17 14? 21.5?? 9.5
#4? 29? 9? 59.0 -21.0
#5? 16 10? 25.0?? 1.0
#6? 30? 3? 70.5 -37.5
#7? 25? 8? 50.5 -17.5
#8? 20 11? 33.5? -2.5
#9? 16? 7? 29.5? -6.5
#10 19 11? 31.0? -1.0

#or
libray(plyr)
mutate(ALL,upper=q3+1.5*(q3-q1),lower=q1-1.5*(q3-q1))
#?? q3 q1 upper lower
#1? 21? 5? 45.0 -19.0
#2? 26? 6? 56.0 -24.0
#3? 17 14? 21.5?? 9.5
#4? 29? 9? 59.0 -21.0
#5? 16 10? 25.0?? 1.0
#6? 30? 3? 70.5 -37.5
#7? 25? 8? 50.5 -17.5
#8? 20 11? 33.5? -2.5
#9? 16? 7? 29.5? -6.5
#10 19 11? 31.0? -1.0


A.K.



----- Original Message -----
From: ramoss <ramine.mossadegh at finra.org>
To: r-help at r-project.org
Cc: 
Sent: Wednesday, April 10, 2013 2:29 PM
Subject: [R] Using PLYR to apply a custom function to a data frame

Hello,

I am still struggling w/ the PLYR syntax.? I am trying to build a customized
function to detect outliers in a data frame based on the interquantile
method.? My data frame is called "ALL" &? I am trying to create
two new
variables in my data frame:
upper=q3+ 1.5*(q3-q1)?  & lower=q1-1.5*(q3-q1).? I already have variables q1
& q3.? How could I create the upper and lower variables using plyr so that
it applies to the whole dataframe.? Thank you for your help.



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and provide commented, minimal, self-contained, reproducible code.

Thanks everyone. The mutate function worked great:

all2<- mutate(all1,upper=p75+1.5*(p75-p25),lower=p25-1.5*(p75-p25))





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