[R] symbols plot
Joerg van den Hoff
j.van_den_hoff at fz-rossendorf.de
Thu Mar 30 09:45:00 CEST 2006
before getting scolded for submitting a (non-)bug report:
when using the 'symbols' function for plotting boxplot data (i.e. using
'boxplots' symbols), I noted that the x/y-position of the symbols is
associated with the center of the box.
while this is obviously natural for a usual plotting symbol (say a
circle or a rectangle), it is probably not desired if one uses the
'boxplots' symbols: looking at such a plot, probably everyone will
assume that y-position is that of the median within the box (in other
words: that one can read off the values of the medians from the y-axis).
the current behaviour is counter-intuitive, I believe, if the
distributions are asymmetrical (and the median is not centered in it's
box). (I even think, that such plots are misinterpreted easily: think
what happens if the median lies very near one of the hinges in one box
and is centered in another one within the same plot and the medians are
actually the same)
in short: I think the 'boxplots' should not be centered at the specified
y-coordinates but rather drawn with a y-coordinate of
y + bxh * (0.5 - bxm)
where bxh and bxm are the second and fifths column of the 'boxplots'
matrix. in this way, the median position is identical to the specified
y-coordinate.
at the very least, I think, the manpage should explicitely state that
all symbols (including boxplots) are positioned with their geometrical
center at the specified coordinates.
right or wrong?
regards,
joerg
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