Message-ID: <1347937901.52268.YahooMailNeo@web142606.mail.bf1.yahoo.com>
Date: 2012-09-18T03:11:41Z
From: arun
Subject: help with calculation from dataframe with multiple entries per sample
In-Reply-To: <1347923753.2562.YahooMailNeo@web142501.mail.bf1.yahoo.com>
HI,
Modified version of my earlier solution:
res1<-tapply(mydata$Mass,mydata$Sample,FUN=function(x) (x[3]-x[2]))
res2<-data.frame(Sample=names(res1),Gain2_3=res1)
?merge(mydata,res2)
#Sample Time Mass Gain2_3
#1????? 1??? 1? 3.0???? 0.3
#2????? 1??? 2? 3.1???? 0.3
#3????? 1??? 3? 3.4???? 0.3
#4????? 2??? 1? 4.0???? 0.1
#5????? 2??? 2? 4.3???? 0.1
#6????? 2??? 3? 4.4???? 0.1
#7????? 3??? 1? 3.0???? 0.3
#8????? 3??? 2? 3.2???? 0.3
#9????? 3??? 3? 3.5???? 0.3
A.K.
----- Original Message -----
From: Julie Lee-Yaw <julleeyaw at yahoo.ca>
To: "r-help at r-project.org" <r-help at r-project.org>
Cc:
Sent: Monday, September 17, 2012 7:15 PM
Subject: [R] help with calculation from dataframe with multiple entries per sample
Hi?
I have a dataframe similar to:
>Sample<-c(1,1,1,2,2,2,3,3,3)
>Time<-c(1,2,3,1,2,3,1,2,3)
>Mass<-c(3,3.1,3.4,4,4.3,4.4,3,3.2,3.5)
>mydata<-as.data.frame(cbind(Sample,Time,Mass))
? Sample Time Mass
1 ? ? ?1 ? ?1 ?3.0
2 ? ? ?1 ? ?2 ?3.1
3 ? ? ?1 ? ?3 ?3.4
4 ? ? ?2 ? ?1 ?4.0
5 ? ? ?2 ? ?2 ?4.3
6 ? ? ?2 ? ?3 ?4.4
7 ? ? ?3 ? ?1 ?3.0
8 ? ? ?3 ? ?2 ?3.2
9 ? ? ?3 ? ?3 ?3.5
where for each sample, I've measured mass at different points in time.?
I now want to calculate the difference between Mass at Time 2 and 3 for each unique Sample and store this as a new variable called "Gain2-3". So in my example three values of 0.3,0.1,0.3 would be calculated for my three unique samples and these values would be repeated in the table according to Sample. I am thus expecting:
>mydata #after adding new variable
? Sample Time MassGain2-3
1 ? ? ?1 ? ?1 ?3.00.3
2 ? ? ?1 ? ?2 ?3.1 0.3
3 ? ? ?1 ? ?3 ?3.4 0.3
4 ? ? ?2 ? ?1 ?4.0 0.1
5 ? ? ?2 ? ?2 ?4.3 0.1
6 ? ? ?2 ? ?3 ?4.4 0.1
7 ? ? ?3 ? ?1 ?3.0 0.3
8 ? ? ?3 ? ?2 ?3.2 0.3
9 ? ? ?3 ? ?3 ?3.5 0.3
Does anyone have any suggestions as to how to do this? I've looked at the various apply functions but I can't seem to make anything work. I'm fairly new to R and would appreciate specific suggestions.?
Thanks!
??? [[alternative HTML version deleted]]
______________________________________________
R-help at r-project.org mailing list
https://stat.ethz.ch/mailman/listinfo/r-help
PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.