[R] comparing 3 datasets

[Deepayan Sarkar]

--- pauljohn at ukans.edu wrote:
> I have 3 datasets with the same variables.  I want
> to find out what
> differences there are between the three, to know if
> an experimental
> condition has an effect.  So I decided first to make
> histograms.  So I
> created this handy "histomatic" function that
> creates a picture with the
> 3 histograms on a single image:
> 
> I thought I was being clever, but in the end, no!
> 
> #read in 3 tables worth
>
NoFlagMod0<-read.table("NoFlagMod0.txt",header=TRUE);
>
RandMastMod0<-read.table("RandMastMod0.txt",header=TRUE);
>
NoMastMod0<-read.table("NoMastMod0.txt",header=TRUE);
> 
> #here's my magical function
> histomatic <- function (s1,s2,s3,var){
>   if (is.numeric (s2[[var]])) {     
>   par(mfrow=c(3,1));
>   hist(s1[[var]],breaks=40,xlab=var);
>   
>   hist(s2[[var]], breaks=40,xlab=var);
>   hist(s3[[var]], breaks=40,xlab=var);
>   }
> }
> #cycle through all the variables, just grab names
> from first set.
> nameList<-names(RandMastMod0);
> par(ask=Yes)
> for (var in nameList)
> histomatic(NoFlagMod0,RandMastMod0,NoMastMod0,var)
> 
> I knew I wanted a pretty fine grained display, so I
> set breaks at 40.
> Other than that, I don't know for sure what else I
> want.
> 
> Here's the problem:
> The histograms shown do not have the same ranges. 
> SInce the datasets
> are slightly different, the ranges displayed are
> different, so they are
> difficult to compare visually.  Is there a solution?


An xlim argument should set the same limits for all
the
histograms. Change your function to:


histomatic <- function (s1,s2,s3,var){
   if (is.numeric (s2[[var]])) {     
   par(mfrow=c(3,1));
   xlim <- range(s1[[var]], s2[[var]], s3[[var]]);
   hist(s1[[var]], breaks=40,xlab=var, xlim = xlim);
   hist(s2[[var]], breaks=40,xlab=var, xlim = xlim);
   hist(s3[[var]], breaks=40,xlab=var, xlim = xlim);
}


This should work.

(You might also consider using the lattice (package in
Devel section) function histogram().)


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