[R] Sorting a Data Frame

[Robert Sherry]

In R, I run the following commands:
     df = data.frame( x=runif(10), y=runif(10) )
     df2 = df[order(x),]

The first, as I would expect, creates a data frame with two columns and 
10 rows. I expect the second to sort the data based upon
the columns x and produce a new data frame, df2, with the same size as 
df. However, the data frame is produces is much larger.
I do not understand what is going on. I am hoping somebody can help me. 
I am also wondering if I should have a comma after
order(x) in the second statement. I do not see a purpose for it but it 
was in an example on the web.

Thanks
Bob