Message-ID: <1355506943.24364.YahooMailNeo@web142606.mail.bf1.yahoo.com>
Date: 2012-12-14T17:42:23Z
From: arun
Subject: Hello R User
In-Reply-To: <CAGC2kj4NOgoXtZq--F5rUbySUS3rGKXUHRbVXWK=sozRk1_nVw@mail.gmail.com>
Hi,
You could also use library(data.table) to do this faster.
dat1<-read.table(text="
ID??? Time
1??? 3
1??? 6
1??? 7
1??? 10
1??? 16
2??? 12
2??? 18
2??? 19
2??? 25
2??? 28
2??? 30
",sep="",header=TRUE)
library(data.table)
dat2<-data.table(dat1)
res<-dat2[,Time1:=c(0,diff(Time)),by=ID]
?head(res,3)
?#? ID Time Time1
#1:? 1??? 3???? 0
#2:? 1??? 6???? 3
#3:? 1??? 7???? 1
#Comparing different approaches:
set.seed(55)
dat3<- data.frame(ID=rep(1:1000,each=500),Value=sample(1:800,5e5,replace=TRUE))
dat4<-data.table(dat3)
system.time(dat3$Value1<-ave(dat3$Value,dat3$ID,FUN=function(x) c(0,diff(x))))
#?? user? system elapsed
?# 0.312?? 0.000?? 0.313
ids<-unique(dat3$ID)
?system.time({
?? for(id in ids){
?? dat3$Value[dat3$ID==id]<-c(0,diff(dat3$Value[dat3$ID==id]))
?? } })
#?? user? system elapsed
# 36.938?? 0.868? 37.873
system.time(dat5<-dat4[,Value1:=c(0,diff(Value)),by=ID])
#?? user? system elapsed
?# 0.036?? 0.000?? 0.037
head(dat5)
#?? ID Value Value1
#1:? 1?? 439????? 0
#2:? 1?? 175?? -264
#3:? 1??? 28?? -147
#4:? 1?? 634??? 606
#5:? 1?? 449?? -185
#6:? 1??? 60?? -389
?head(dat3)
#? ID Value Value1
#1? 1???? 0????? 0
#2? 1? -264?? -264
#3? 1? -147?? -147
#4? 1?? 606??? 606
#5? 1? -185?? -185
#6? 1? -389?? -389
A.K.
----- Original Message -----
From: bibek sharma <mbhpathak at gmail.com>
To: R help <r-help at r-project.org>
Cc:
Sent: Friday, December 14, 2012 10:51 AM
Subject: [R] Hello R User
Hello R User,
In the sample data given below, time is recorded for each id
subsequently. For the analysis, for each id, I would like to set 1st
recorded time to zero and thereafter find the difference from previous
time. I.e. for ID==1, I would like to see Time=0,3,1,3,6. This needs
to be implemented to big data set.
Any suggestions are much appreciated!
Thanks,
Bibek
ID??? Time
1??? 3
1??? 6
1??? 7
1??? 10
1??? 16
2??? 12
2??? 18
2??? 19
2??? 25
2??? 28
2??? 30
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