[R] help with calculation from dataframe with multiple entries per sample

[William Dunlap]

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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> 
> 
> ______________________________________________
> 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.