Hi Sandy, The way I'd describe it is that you expected the width parameter of the position adjustment to be relative to the binwidth of the histogram - but it's actually absolute, and it has to be this way because there's currently no way for the position adjustment to know about the parameters of the geom.
Hadley On Wed, Dec 1, 2010 at 10:07 AM, Small Sandy (NHS Greater Glasgow & Clyde) <sandy.sm...@nhs.net> wrote: > Sorry this should have ben to the whole list: > > Hadley > > I think I've sorted it out in my head but for the record, and just to be > sure... > I guess what I was expecting was that the width parameter would be > independent of binwidth. Thus a width parameter of 0.5 would always indicate > an overlap of half the bar. In fact the width is determined as a fraction of > the binwidth, so if width is greater than binwidth the overlap will be with > adjacent bins not the bin it actually corresponds to. > So in my example you can completely separate the data by putting > ggplot(data=dafr, aes(x = d1, fill=d2)) + geom_histogram(binwidth = 2, > position = position_dodge(width=7)) > Obviously this isn't helpful. > I think the rules are: > 1. the width of each bar equals binwidth divided by number of fill factors > (in my case two) > 2. total width of the visible bars would be centred on the centre of the bin > 3. overlap of the visible bars is governed by the width parameter of > position_dodge with 0 being complete overlap and binwidth being complete (but > touching) separation (More than binwidth would then mean space between the > bars - and presumably overlap with adjacent bars - I don't think this would > ever be useful). > Hope this makes sense. > Sandy > > Sandy Small > Clinical Physicist > NHS Forth Valley > (Tel: 01324567002) > and > NHS Greater Glasgow and Clyde > (Tel: 01412114592) > ________________________________________ > From: h.wick...@gmail.com [h.wick...@gmail.com] On Behalf Of Hadley Wickham > [had...@rice.edu] > Sent: 01 December 2010 14:27 > To: Small Sandy (NHS Greater Glasgow & Clyde) > Cc: ONKELINX, Thierry; r-help@r-project.org > Subject: Re: [R] ggplot2 histograms > >> However if you do: >> ggplot(data=dafr, aes(x = d1, fill=d2)) + geom_histogram(binwidth = 1, >> position = position_dodge(width=0.99)) >> >> The position of first bin which goes from 0-2 appears to start at about 0.2 >> (I accept that there is some "white space" to the left of this) while the >> position of the last bin (16-18) appears to start at about 15.8, so the >> whole histogram seems to be wrongly compressed into the scale. In my real >> data which has potentially 250 bins the problem becomes much more >> pronounced. Has any one else noticed this? Is there a work around? > > What do you expect this to do? The bars are one unit wide, but you've > told position_dodge to treat them like they're only 0.99 units wide. > > Hadley > > -- > Assistant Professor / Dobelman Family Junior Chair > Department of Statistics / Rice University > http://had.co.nz/ > > ******************************************************************************************************************** > > This message may contain confidential information. If yo...{{dropped:21}} > > ______________________________________________ > R-help@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. > -- Assistant Professor / Dobelman Family Junior Chair Department of Statistics / Rice University http://had.co.nz/ ______________________________________________ R-help@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.
