[R] Removing rows w/ smaller value from data frame

[arun]

Hi,
Try:
datNew<- read.table(text="
activity    max_dt
A            2013-03-05
B            2013-03-28
A            2013-03-28
C            2013-03-28
B            2013-03-01
",sep="",header=TRUE,stringsAsFactors=FALSE)
datNew$max_dt<- as.Date(datNew$max_dt)
 aggregate(max_dt~activity,data=datNew,max)
#  activity     max_dt
#1        A 2013-03-28
#2        B 2013-03-28
#3        C 2013-03-28
#or

library(plyr)
 ddply(datNew,.(activity),summarize, max_dt=max(max_dt))
#  activity     max_dt
#1        A 2013-03-28
#2        B 2013-03-28
#3        C 2013-03-28
#or 
ddply(datNew,.(activity),summarize, max_dt=tail(sort(max_dt),1))
#  activity     max_dt
#1        A 2013-03-28
#2        B 2013-03-28
#3        C 2013-03-28


A.K.

----- Original Message -----
From: ramoss <ramine.mossadegh at finra.org>
To: r-help at r-project.org
Cc: 
Sent: Thursday, May 23, 2013 10:23 AM
Subject: [R] Removing rows w/ smaller value from data frame

Hello,

I have a column called max_date in my data frame and I only want to keep the
bigger values for the same activity.  How can I do that?

data frame:

activity    max_dt
A            2013-03-05
B             2013-03-28
A             2013-03-28
C             2013-03-28
B             2013-03-01

Thank you for your help



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