st: Computing and allocating time intervals in a wide dataset

[Thomas Speidel <thomas@tmbx.com>]

I am attempting to compute several time points to calculate the  
interval (years) between the start and the end of an activity and to  
assign that interval to its relevant age group.  For example, given  
the following dataset:

    id   activity   start   stop
     1          1       6     15
     1          2      22     25
     1          3      15     16
     1          4      22     28
     1          5      30      .
     1          6       .      .
     2          1      53     69
     2          2      69     79

I am trying to derive the following:

    id   activity   start   stop   grp_0_17   grp_1~24   grp_2~44    
grp_4~64   grp_6~81
     1          1       6     15          9          0          0      
     0          0
     1          2      22     25          0        2.5         .5      
     0          0
     1          3      15     16          1          0          0      
     0          0
     1          4      22     28          0        2.5        3.5      
     0          0
     1          5      30      .          0          0          1      
     0          0
     1          6       .      .          .          .          .      
     .          .
     2          1      53     69          0          0          0      
  11.5        4.5
     2          2      69     79          0          0          0      
     0         10

The age groups are:
[0.5, 17.5]
[17.6, 24.5]
[24.6, 44.5]
[44.6, 64.5]
[64.6, 81]

If the dataset was in long format as above, it would not be terribly  
hard. To slightly complicate things is the fact that the interval may  
need to be correctly allocated when it falls between two or more age  
groups.  However, my data is in wide format (single observation per  
row) making it a nightmare to even check or troubleshoot my code (I  
have 40 activities per id), and the data is so large that I am  
reluctant to reshape it.
This is what the dataset above would look like:

    id   start1   stop1   start2   stop2   start3   stop3   start4    
stop4   start5   stop5   start6   stop6
     1        6      15       22      25       15      16       22     
  28       30       .        .       .
     2       53      69       69      79        .       .        .     
   .        .       .        .       .

-The activities do not necessarily follow a temporal sequence (e.g.  
3rd observation on top)
-While the example does not show that, every id has exactly 40  
activities, even though many of them may be completing missing.
-Whenever a start is present but its corresponding stop is missing (as  
in the 6th obs. on top), it means that at the time of the study the  
person was still performing that activity, hence stop would be a  
variable called ageref. If start==ageref, then the interval would be  
approximated as 1 year.

I would appreciate any feedback on how to best tackle this problem.

Thanks,
Thomas Speidel


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