How to output graphics while maintaining alphabetical order

Question

I have a script to output graphic files via png()

the filename is based on a value(p) and the observation id ID(numerical value).

> summary(p)
   Min. 1st Qu.  Median    Mean 3rd Qu.    Max. 
0.05328 0.10770 0.20830 0.31140 0.42360 0.99990 
> summary(id)
     Min.   1st Qu.    Median      Mean   3rd Qu.      Max. 
100000000 114100000 130400000 186100000 287300000 4513000
> str(p)
 num [1:223] 0.175 0.1499 0.156 0.0636 0.1628 ...
> str(id)
 int [1:223] 100037005 100270001 100270002 100801001 101910002 101910003 101910007 102510001 103630003 103630005 ...

so that

png(paste(p," - ", id,".png)

My goal is that the files in the output directory, when sorted by name, are in increasing p order, while the id is still in the filename.

I cant understand why but the sort order gets messed up, like in the attached screenshot.

Any ideas how I can get the output i need? A transformation of p is OK as long as it is easy to track back to the original value, and both p and id must be in the file name. I'm on Ubuntu 11.10.

Thanks a lot

Answer 1

You could try to make sure the p values are all the same length when converted to strings. Use sprintf:

pstring = sprintf("%010.8f",p)

will create a string with exactly 8 decimals, leading and trailing zeroes, and for values 0 to 1 will always be 10 characters long (zero, point, then eight decimals).

sprintf("%010.8f",runif(100))

should show you what it does.

Adjust the format according to your taste, simmer gently, serve.