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-boun...@r-project.org [mailto:r-help-boun...@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 <jullee...@yahoo.ca>
> To: "r-help@r-project.org" <r-help@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.
>
>
> ______________________________________________
> R-help@r-project.org mailing list
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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.
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and provide commented, minimal, self-contained, reproducible code.
