st: Graphing longitudinal profiles

[Thomas Speidel <thomas@tmbx.com>]

I am having difficulties creating a connected line graph for a 
longitudinal dataset.  Here's an example of a simplified dataset:

. list, clean noobs

    id   time   value
    84      0      15
    84      1      18
    84      2      17
    88      0      19
    88      1       .
    88      2       .
    93      0      14
    93      1      19
    93      2      19
    94      0      16
    94      1      20
    94      2      20
    97      0      13
    97      1       .
    97      2       .
    98      0      17
    98      1      19
    98      2      20
    99      0      17
    99      1      18
    99      2      20

. sort id time
. twoway line value time, connect(L)
[graph]

Notice the vertical line going from 13 to 19 on the y-axis. Why?
I read Nick Cox's FAQ: 
http://www.stata.com/support/faqs/graphics/connect.html and I feel the 
solution to my problem is buried somewhere there.  Yet, I tried all 
sorts of "sorts" and the problem remains.
I neeed line segments for each id, all on the same graph.

Thanks,
Thomas Speidel
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