[R] bar order using lattice barchart()

[Tim Clark]

Greg,

Thanks for the great explanation.  Knowing the philosophy behind these kind of things really helps avoid problems in the future. 

Aloha,

Tim

Tim Clark
Department of Zoology 
University of Hawaii


--- On Thu, 5/6/10, Greg Snow <Greg.Snow at imail.org> wrote:

> From: Greg Snow <Greg.Snow at imail.org>
> Subject: RE: [R] bar order using lattice barchart()
> To: "Tim Clark" <mudiver1200 at yahoo.com>, "r-help at r-project.org" <r-help at r-project.org>
> Date: Thursday, May 6, 2010, 7:51 AM
> The short answer to your query is
> ?reorder
> 
> The longer answer (or a longer answer) gets into a bit of
> philosophy (so feel free to go back to the short answer and
> skip this if you don't want to get into the philosophy, you
> have been warned).  Let's start with the question: is
> the order of the bars a property of the graph/analysis? The
> dataset as a whole? Or the individual variable?
> 
> Some programs take the first approach, the order is a
> property of the graph or analysis, these programs have you
> specify things like the order at the time of creating the
> graph or doing the analysis.  I don't like this
> approach because it seems to me that this should be more
> inherent to the data than the output, also this means that
> you have to keep specifying the order for every
> graph/analysis and I am too lazy to like that.
> 
> Your attempt was number 2, the order should be a property
> of the dataset.  For your example this makes a lot of
> sense, you want x ordered by y.  But this does not
> generalize to some other situations, so is not the standard
> for R.
> 
> My favorite (and what is used in R, so apparently I'm not
> the only one) is to have things like the order be a property
> of the individual variable (x in this case).  Your data
> frame will have x as a factor by default (and even if you
> specifically told R to not convert it to a factor, then many
> plotting/analysis functions will still convert it to a
> factor).  If you don't specify the order of the factor
> levels then the default is to do it alphabetically and this
> will be used by plotting/analysis functions regardless of
> the order in the data set.  One of the easier ways to
> change the order of the factor levels, especially for a case
> like yours is using the reoder function, try something
> like:
> 
> > xy$x <- reorder( xy$x, xy$y )
> 
> You won't see any obvious differences when you print the
> data frame, but if you print just x then you should and your
> plots should come out the way that you want now.
> 
> You did ask "why?" and were warned.  Hope this helps,
> 
> -- 
> Gregory (Greg) L. Snow Ph.D.
> Statistical Data Center
> Intermountain Healthcare
> greg.snow at imail.org
> 801.408.8111
> 
> 
> > -----Original Message-----
> > From: r-help-bounces at r-project.org
> [mailto:r-help-bounces at r-
> > project.org] On Behalf Of Tim Clark
> > Sent: Wednesday, May 05, 2010 8:57 PM
> > To: r-help at r-project.org
> > Subject: [R] bar order using lattice barchart()
> > 
> > Dear List,
> > 
> > I am want to plot my data in increasing order using
> the lattice
> > barchart() function.  I used order() to put my
> data in the order I
> > want, but when I plot it I get the original order of
> the data.  I think
> > this has to do with the row index number since order()
> does not re-
> > number the rows in the new order but instead keeps the
> original row
> > numbers and puts them in a different order.  For
> example:
> > 
> > xy<-data.frame(x=letters[1:5],y=c(3,9,2,1,10))
> > 
> > #This produces a dataframe in alphebitical order with
> row numbers in
> > #numerical order.
> > > xy
> >   x     
>    y
> > 1 a  8.921657
> > 2 b 10.314625
> > 3 c  9.531537
> > 4 d 10.818563
> > 5 e  9.084872
> > 
> > 
> > #If I re-order the data based on the value of y
> > 
> > xy<-xy[order(y),]
> > 
> > #I get a dataframe ordered by y but the row numbers
> are still in
> > #alphebetical order based on x
> > > xy
> >   x     
>    y
> > 1 a  8.921657
> > 5 e  9.084872
> > 3 c  9.531537
> > 2 b 10.314625
> > 4 d 10.818563
> > 
> > #I then try to plot the data and it plots it in
> alphabetical instead of
> > #numeric order
> > library(lattice)
> > barchart(y~x, data=xy)
> > 
> > 
> > 
> > Why are the rows not re-indexed, and how do I get
> barchart() to plot my
> > data in increasing numeric order?
> > 
> > Thanks,
> > 
> > Tim
> > 
> > 
> > 
> > 
> > Tim Clark
> > Department of Zoology
> > University of Hawaii
> > 
> > ______________________________________________
> > 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.
>