Ordering bars in barplots

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by() will sort on the levels of `class', so I think what you need to do is 
ensure that `class' has its levels sorted numerically.  Try

df$class <- factor(as.numeric(as.character(df$class)))

to do that.  Then to sort the df by numerical class you could use

df <- df[sort.list(unclass(df$class)), ]

It might be easier just to make class a number for some purposes at
least (just omit the factor() above).

I have a dataframe such that when I enter the dataframe name at the R prompt
and see the data, the order of the data is correct (ie. what I want -
ordered numerically by the factor, class).  The table is akin to the
following:

df: (dataframe = df)
uniqueID  class	age
a	   1	32
b	   1	21
c	   1	13
d	   1	11
e	   3	15
f	   3	16
g	   3	31
h	   3	25
i	   4	23
j	   4	32
k	   4	31
l	   7	11
m	   7	6
n	   7	20
o	  10	19
p	  10	25
q	  10	42
.
.
.

uniqueID and class are factors. Yesterday I think I managed to figure out
how to arrange the column "class" in "numerical" order (when it lists) even
though it's a "character" factor.  (although feel free to pipe in an answer
on that too - since I was trying a lot of different things!)

Now, when I execute the following command:

barplot(by(df[,"age"],df$class,FUN=function(x) quantile(x,0.95)))

the x-labels or "class" of each bar is in *character* order, not *numerical
order.

Is there a way to rearrage this so that each bar label (categorical x-label)
is in numerical order?

Thanks in advance!!!
Best,
Scott

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Brian D. Ripley,                  ripley at stats.ox.ac.uk
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