[R] comparing 3 datasets

Jonathan Baron baron at cattell.psych.upenn.edu
Wed Jun 20 03:25:51 CEST 2001

>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
>#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.
>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?
>Paul E. Johnson                       email: pauljohn at ukans.edu

I can solve this problem, not the other one.  Here is an example,
the results of which are about half way down the page on:

The critical thing is using the different format for "breaks,"
which specifies the cutoffs rather than the number of them.  This
way you can use the same cutoffs for all the histograms.


Jon Baron

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