st: Sorting by and testing within subsets

[steinar.fossedal@skandiabanken.no]

Greetings, Statalisters.

 

I am currently working with a dataset which I suspect contains numerous errors - faulty settings of classification variables and such. Thus I want to run different logical tests to sort out which observations I need to have a closer look at.

 

The dataset is set up like this:

 

PersonID           PersonInfo

1                      A

2                      A

2                      A

2                      B

3                      A

3                      A

4                      B

5                      C

6                      C

.                       .

.                       .

 

 

I am interested in checking wether the information registered on a person is consistent. In the example above (sorry I can't give you the real deal, but it's sensitive information) we can see that Person 2 is registered twice as A and once as B. Person three is registered twice, both times as A.

 

What I would like is a list which shows the persons who have conflicting PersonInfo, one line for each person (Only person 2 in the example above). I figure I have to sort the PersonID into groups somehow and then do a check within each group if the registered information is consistent. However I'm having a hard time getting Stata to do so. My best suggestion so far would be

 

bysort PersonID: gen dummy=1 if( <not all values of PersonInfo within the group are equal> )

 

but I'm not able to specify what goes in the if-statement since I cannot seem to find any function which counts number of distinct values. Also listing the troublesome observations only one line per person seems to be out of my grasp. Any comments or suggestions you might have would be greatly appreciated.

 

Sincerely yours,

 

Steinar Fossedal