Re: [R] arrows and points for error bars

From: Simon Pickett <>
Date: Fri 20 Oct 2006 - 16:33:31 GMT

Hi there,
I did what Peter Dalgaard very kindly suggested and saved it as a pdf and viewed it using adobe, which as if by magic resolves the problem. It must have been a pixel issue with the r graphics device. Sorry to have wasted your time, thanks for your help, always appreciated. Simon.

> It would be very helpful to have a reproducible example, including the OS
> and graphics device used.
> For example, this may only happen with certain values of 'pch' -- e.g.
> some graphics devices (pdf is one) plot circles using completely different
> code from squares. And we frequently see reports of problems with R
> graphics where the bug is in the viewer software or the including
> application (Word being notorious for mis-rendering WMF files).
> On Fri, 20 Oct 2006, Peter Dalgaard wrote:
>> "Simon Pickett" <> writes:
>>> Hello everyone,
>>> I have successfully made an error bar graph using the points() command
>>> with the arrows() command to maually add on the standard errors.
>>> However, one slightly annoying feature of using this method is that the
>>> points dont line up exactly with the arrows (if you look carefully the
>>> points are never perfectly in the centre of the arrow), even when you
>>> move
>>> the arrows around in an attempt to correct this.
>> Is this a pixelization issue? If the line is an odd number of pixels
>> wide and the point is an even number of pixels across, then there is
>> just no way to line them up. It should go away with increased
>> resolution, e.g. when plotting to pdf() and printing on a laser
>> printer.
>>> Secondly I cant seem to force the points to appear on top of the arrows
>>> i.e. with the arrows behind the points. Uing ADD=TRUE to either command
>>> wont work.
>> Plot the points last and use a filled symbol, or pch %in% 21:25 with
>> bg="white". (example(points) is generally helpful in these matters)
>>> Does anyone have any solutions to this problem, or maybe even a
>>> different
>>> way of making error plots?
>>> Sorry if this seems a bit pedantic, but it would be great if I could
>>> resolve this problem and so enable me to use R for publication standard
>>> graphs...
>>> Thanks everyone :-)
> --
> Brian D. Ripley,
> Professor of Applied Statistics,
> University of Oxford, Tel: +44 1865 272861 (self)
> 1 South Parks Road, +44 1865 272866 (PA)
> Oxford OX1 3TG, UK Fax: +44 1865 272595

Simon Pickett
PhD student
Centre For Ecology and Conservation
Tremough Campus
University of Exeter in Cornwall
Tel 01326371852 mailing list PLEASE do read the posting guide and provide commented, minimal, self-contained, reproducible code. Received on Sat Oct 21 02:46:48 2006

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