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Hi-
I'm trying to add a column to a dataset that is dependent on a value from a
previous record within the dataset.
Given the following input data:
data unit_status;
input unit $ date date9. hour status $;
datalines;
333 01apr2009 1 OFF
333 01apr2009 2 OFF
333 01apr2009 3 RAMP
333 01apr2009 4 RAMP
333 01apr2009 5 RAMP
333 01apr2009 6 ON
333 01apr2009 7 ON
333 01apr2009 8 ON
333 01apr2009 9 RAMP
333 01apr2009 10 RAMP
333 01apr2009 11 ON
333 01apr2009 12 OFF
334 01apr2009 1 OFF
334 01apr2009 2 OFF
334 01apr2009 3 OFF
334 01apr2009 4 RAMP
334 01apr2009 5 RAMP
334 01apr2009 6 ON
334 01apr2009 7 ON
334 01apr2009 8 ON
334 01apr2009 9 RAMP
334 01apr2009 10 ON
334 01apr2009 11 ON
334 01apr2009 12 RAMP
;
I would like to add another column called prev_status which will hold the
status of each unit prior to (and distinct from) its current status. This
would involve:
1.Checking the current status (i.e., RAMP)
2.Look at the status from the prior record. If the prior status is
different from the current status (i.e. OFF ne RAMP) then save the prior
status in the prev_status column (prev_status = OFF).
3.If the prior status is the same as the current status, step back another
record and check again for inequality.
4. If looking at the first record for a specific unit, prev_stat = null.
I believe this should use some form of iteration of the lagn() function
along with the ifc() function. Unfortunately, I've been unable to
successfully accomplish this.
Thanks for any help you can offer!
Ben
Desired Output:
data unit_status_2;
input unit $ date date9. hour status $ prev_status $;
datalines;
333 01apr2009 1 OFF .
333 01apr2009 2 OFF .
333 01apr2009 3 RAMP OFF
333 01apr2009 4 RAMP OFF
333 01apr2009 5 RAMP OFF
333 01apr2009 6 ON RAMP
333 01apr2009 7 ON RAMP
333 01apr2009 8 ON RAMP
333 01apr2009 9 RAMP ON
333 01apr2009 10 RAMP ON
333 01apr2009 11 ON RAMP
333 01apr2009 12 OFF ON
334 01apr2009 1 OFF .
334 01apr2009 2 OFF .
334 01apr2009 3 RAMP OFF
334 01apr2009 4 RAMP OFF
334 01apr2009 5 RAMP OFF
334 01apr2009 6 ON RAMP
334 01apr2009 7 ON RAMP
334 01apr2009 8 ON RAMP
334 01apr2009 9 RAMP ON
334 01apr2009 10 RAMP ON
334 01apr2009 11 ON RAMP
334 01apr2009 12 OFF ON
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