[R] font size relative to graphic

[David Winsemius]

On Apr 24, 2009, at 4:10 PM, Mike Miller wrote:

> On Fri, 24 Apr 2009, David Winsemius wrote:
>
>> On Apr 24, 2009, at 3:14 PM, Mike Miller wrote:
>>
>>> I am printing numbers onto horizontal bars in a bar plots, but I  
>>> am finding it difficult to make the number always the right size.   
>>> If there are more bars, the bars get narrower and the font is too  
>>> big.  I also find that if I change the size of the graph, the bars  
>>> will get wider or narrower and the font stays about the same  
>>> size.  The result depends on whether I view the graph in X11 or in  
>>> postscript.
>>> Is there a way to specify font size relative to bar width, or at  
>>> least specify font size relative to graph coordinates?
>>> Here's a bit of what I've been doing:
>>> x.bar.plot <- barplot(as.matrix(x), horiz=TRUE, beside=TRUE,  
>>> xlim=c(0,100), xlab="Score", las=1)
>>> text(as.matrix(x), x.bar.plot-.07,  
>>> as.character(as.matrix(round(x))), pos=2, col="black")
>>> The "-.07" is something I added to make the numbers align well  
>>> with the bars under one condition, but it doesn't always help.
>>> Any tips would be greatly appreciated.  Thanks in advance.
>>
>> The values returned from the barplot function are the locations of  
>> the bars. Why not call barplot, collect the values, and then use  
>> the length of the result to determine your sizes and widths?
>
> That is exactly the kind of thing I want to do, but I don't know how  
> the font size can be specified so that it fits.  My bars are  
> horizontal and yours (from code below) are vertical.  Your barplot  
> output was called "mp" and mine was called "x.bar.plot" and here is  
> what they looked like:
>
>> mp
>     [,1] [,2] [,3] [,4] [,5]
> [1,]  1.5  6.5 11.5 16.5 21.5
> [2,]  2.5  7.5 12.5 17.5 22.5
> [3,]  3.5  8.5 13.5 18.5 23.5
> [4,]  4.5  9.5 14.5 19.5 24.5
>
>> x.bar.plot
>     [,1] [,2] [,3] [,4] [,5] [,6] [,7] [,8] [,9] [,10] [,11] [,12]
> [1,]  1.5  4.5  7.5 10.5 13.5 16.5 19.5 22.5 25.5  28.5  31.5  34.5
> [2,]  2.5  5.5  8.5 11.5 14.5 17.5 20.5 23.5 26.5  29.5  32.5  35.5
>
> They are pretty similar numbers.  It seems that [1,1] element is  
> always 1.5 and consecutive elements in the same column differ by  
> 1.0, but in the rows we see something different: mine are 3.0 apart  
> and yours are 5.0 apart.  So what does this tell me?  I think fonts  
> are specified in points which correspond to 1/72 inches, while bars  
> are specified in coordinates that are independent of inches.  So I  
> need to know how coordinates correspond to inches before I can get  
> this fixed.

They do not correspond to inches, but the the numeric scale of the  
values. Here is your plot with the numbers moved so they are to the  
right of the bar ends:

txt <- "1.5  4.5  7.5 10.5 13.5 16.5 19.5 22.5 25.5  28.5  31.5  34.5
  2.5  5.5  8.5 11.5 14.5 17.5 20.5 23.5 26.5  29.5  32.5  35.5"
x <- read.table(textConnection(txt), header=FALSE)

x.bar.plot <- barplot(as.matrix(x), horiz=TRUE, beside=TRUE,  
xlim=c(0,100), xlab="Score", las=1)
text(as.matrix(x+6), x.bar.plot-.07,  
as.character(as.matrix(round(x))), pos=2, col="black")

# the rounding is what makes the dissimilar bars labeled with the same  
numbers, ... yecch.

Haven't figured out what the requirements on sizing really are;  but  
here is an example you might play with:

text(as.matrix(x+6), x.bar.plot-.07,  
as.character(as.matrix(round(x))), pos=2, col="black",
     cex= 24/length(as.matrix(x)))


David Winsemius, MD
Heritage Laboratories
West Hartford, CT