[R] re shaping "long-form" longitudinal data from sql query

Tubin sredmonson at yahoo.com
Thu Apr 24 20:13:46 CEST 2008

hi, I'm a total noob who is having to ramp up to full speed very quickly due
to an unfortunate abrupt staffing change at my job :)

I have longitudinal data that looks like this:
               PID             OBSDATE                DaysAgo CleanValue  
1  1410164934000610  8/17/2004 13:03:38    1345        6.2        HGBA1C
2  1410164934000610 11/16/2004 10:39:51    1254        7.1        HGBA1C

I'd like to end up with a wide-format table like:
PID     OBSDATE.1    DaysAgo.1    CleanValue.1 [...] OBSDATE.n   DaysAgo.n   

The problem:  Every patient's on a different schedule, so there's no natural
timevar value to reshape with.

My solution involved creating another column for the timevar and looping
through the dataframe to populate that column with correct values; however,
it's a pretty big table and so the loop runs really slowly.  I need to do
this particular operation on quite a few datafiles on a regular basis, and
my database keeps getting bigger - so I anticipate this solution won't be
ideal in the future.

Can anyone recommend a more efficient solution?  

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