expressions as axis labels

[moved to R-devel]

On Sat, 25 May 2002, Patrick Buetzberger wrote:

Dear colleagues,

I often use chemical formulas to label my x-axis, e.g. in barplots. I
used to do this like the following example and it worked just fine:

<snip>

The important point is the x-axis here: before we installed the new R
1.5 on our workstations, the chemical formulas were properly aligned and
looked well. Ever since, if I use the exact same procedure, I get the
graphic but the chemical formulas are not aligned horizontally properly
anymore: e.g. Mg^{2+''} or NO[3]^{-''} are a bit higher than F^{-''} or
H^{+''} (it seems to depend on whether there is a subscript or a letter
with a part below the main line like a 'g').
I didin't find any hint on the r-project homepage. I don't know if we
forgot some feature when newly installing R or if something changed in
version 1.5.

I think something changed.  In the NEWS file we have

o       The vertical alignment of mathematical annotations was wrong.
        When a vertical adjustment was not given, it was bottom-adjusting
        i.e,. it was treating adj=0 as adj=c(0, 0).  It now treats
        adj=0 as adj=c(0, 0.5) as for "normal" text. (PR#1302)

and I expect this is responsible.  

That change indeed is reasonable, but I don't think it is this
particular change (at least as documented) that makes Patrick's example
doesn't work any more.

It looks to me as if R is now trying to center the expressions vertically. 

Right for text() and friends, but not for axis(), see the example below,
and maybe this is a bug (Paul?). Anyway, fixing this bug (?) won't
change much for Patrick's example.

This is also consistent with the previous reply that suggested putting blank 
subscripts on everything as a work-around.

If sub- or superscripts are a expression, space is added below
respective above that expression (if not already done before), so
complex formulas can be generated. And, at least for me, the result is
somehow expected.

I am very surprised and wondered why Patrick's example worked in
R-1.4.1.
Without having looked into the code, there must have been something
fuzzy that is broken since R-1.5.0.

I don't think there's a complete fix for this, since sometimes people want
expressions aligned on their actual vertical centers and sometimes on the
center of the main line of text (as you do).

Here an example on the alignments:

 plot(1:12, type="n", axes=FALSE)

 expr <- expression(F^{-''}, Cl^{-''}, NO[2]^{-''}, NO[3]^{-''}, 
    PO[4]^{3-''}, SO[4]^{2-''}, Na^{+''}, NH[4]^{+''}, K^{+''},
    Mg^{2+''}, Ca^{2+''}, H^{+''})

 axis(1, 1:12, lab=expr)  # the "problem"

 text(1:12, 3, expr) # adj=c(0.5, 0.5), the default for text()

# This looks like the x-axis annotation:
 text(1:12, 5, expr, adj=c(0.5, 0)) 

# And this is all in *one* formula, as Patrick would like to get it
somehow.
# Only a guess: Was there something like a "coerce to one formula" in
R-1.4.1?

 text(6, 9, 
    labels = expression(F^{-''} * Cl^{-''} * NO[2]^{-''} * NO[3]^{-''} * 
    PO[4]^{3-''} * SO[4]^{2-''} * Na^{+''} * NH[4]^{+''} * K^{+''} *
    Mg^{2+''} * Ca^{2+''} * H^{+''}))


I am sure, Paul will get the point in less than a second.

Uwe Ligges
-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-
r-devel mailing list -- Read http://www.ci.tuwien.ac.at/~hornik/R/R-FAQ.html
Send "info", "help", or "[un]subscribe"
(in the "body", not the subject !)  To: r-devel-request@stat.math.ethz.ch
_._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._