help with calculation from dataframe with multiple entries per sample

Tue, Sep 18, 2012 8:12 AM

The following works even when the input data frame has its rows
scrambled.  It does not currently check that there is exactly one entry
in each sample for Time==2 and Time==3.

within(mydata, 
            `Gain2-3` <- ave(seq_along(Sample),
                                          Sample,
                                          FUN=function(i) {
                                             L2 <- Time[i]==2
                                             L3 <- Time[i]==3
                                             Mass[i][L3] - Mass[i][L2] }))

Bill Dunlap
Spotfire, TIBCO Software
wdunlap tibco.com

-----Original Message-----
From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-project.org] On Behalf
Of arun
Sent: Monday, September 17, 2012 8:12 PM
To: Julie Lee-Yaw
Cc: R help
Subject: Re: [R] help with calculation from dataframe with multiple entries per sample

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]]

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PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.

help with calculation from dataframe with multiple entries per sample

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