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

[arun]

>From your email, it seems like aggregate() is working.

Could you please provide the sessionInfo()?
My guess is that some other loaded library is masking the summarize().
For example, if I load
library(Hmisc)
#The following object is masked from ‘package:plyr’:
#
 #   is.discrete, summarize


ddply(datNew,.(activity),summarize, max_dt=max(max_dt)) #
#Error in is.list(by) : 'by' is missing
 ddply(datNew,.(activity),plyr::summarize,max_dt=max(max_dt))
#  activity     max_dt
#1        A 2013-03-28
#2        B 2013-03-28
#3        C 2013-03-28
A.K.


----- Original Message -----
From: "Mossadegh, Ramine N." <Ramine.Mossadegh at finra.org>
To: arun <smartpink111 at yahoo.com>
Cc: 
Sent: Thursday, May 23, 2013 10:44 AM
Subject: RE: [R] Removing rows w/ smaller value from data frame

Thank but I get : Error in is.list(by) : 'by' is missing
When I tried ddply(datNew,.(activity),summarize, max_dt=max(max_dt))

-----Original Message-----
From: arun [mailto:smartpink111 at yahoo.com] 
Sent: Thursday, May 23, 2013 10:40 AM
To: Mossadegh, Ramine N.
Cc: R help
Subject: Re: [R] Removing rows w/ smaller value from data frame

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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