pch and mkh bug PR#225

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Subject: pch and mkh bug PR#225
Date: Thu 15 Jul 1999 - 12:28:02 EST

Message-Id: <199907150228.EAA02869@pubhealth.ku.dk>

I am sorry about the problem caused by my first attempt at reporting a
bug. This is a followup to my report PR#225, hopefully being more
useful. By not I have a better understanding of the problems being

I wish to report one bug relating to plot character and to mention two
other possible bugs (these may relate to differences between R and S)
I have noticed with R. We have recently installed R and I am
converting some scripts I had previously used with a very old version
of S (not Splus). The R version information is:

platform sparc-sun-solaris2.5.1
arch sparc
os solaris2.5.1
system sparc, solaris2.5.1
status.rev 0
major 0
minor 64.2
year 1999
month July
day 3
language R

In the following I will be quoting some extracts from R A Becker, J M
Chambers and A R Wilks _The New S Language_, Wadsworth & Brooks/Cole
1988, isbn 0-534-09192-X. We have a copy of this book since, although
our departmental server did not update from S to Splus, the campus
server did. I am using this as an authority to report some of the
following as being bugs.

(1) First the boxes drawn using `points()' via the following example

Y <- c(13.75, 10.50, 7.25, 4.0)
X <- c(1, 2, 3, 4)

are of a size that indicated that the mkh value is being ignored (the
upper set of boxes). This can be fixed by using cex (the lower set of
boxes). However, the S manual states that `mkh' gives the height in
inches of mark symbols drawn when `pch' is given as a number. This
comment is also made in the help for the `par' function within R. This
would appear to be a bug, using `cex' is correct only when giving a

(2) The plotting of axis labels on an axis becomes confused if the
`at' vector is descending. For exaample, consider the following:

labels <- c("A", "B", "C", "D")
Y <- c(13.75, 10.50, 7.25, 4.0)
X <- c(1, 2, 3, 4)

According to the S manual `label[i]' is plotted at coordinate `at[i]'.
Although S (or R) plot the vector in ascending order this still worked
(in old S, anyway), it may have been a feature. However, R appears to
sort `at[i]' but not do a corresponding sort on label[i]. The R help
does not make the statement about plotting `label[i]' at coordinate
`at[i]', so this may be a difference between S and R. It can be
overcome by appropriate pre-sorting of the two vectors.

(3) The use of `mtext' only works for a string, not for a vector of
strings. For example, the following commands.

labels <- c("A", "B", "C", "D")
Y <- c(13.75, 10.50, 7.25, 4.0)
X <- c(1, 2, 3, 4)
mtext(text=labels, side=4, line=0.5, at=Y)

plots only the first of the elements of `labels'. Again, this may
reflect a difference between S and R. The S manual states that `text'
is a character vector to be plotted and `at' is an optional vector of
positions. However, the R help states that `text' is a character
string and `at' gives the location in user coordiates. This can be
overcome by plotting `labels[i]' at `at[i]' within a loop.

Stephen Harker                                        s-harker@adfa.edu.au
School of Physics               Baloney Baffles brains: Eric Frank Russell
University College                http://www.adfa.edu.au/physics/s-harker/

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