I am learning horse-colic dataset.
there are 2 types of values in column 2, 1 and 9.
dose that mean a record (a horse) is 1 year old or 9 years old?
According to the documentation on the link you provided:
2: Age 1 = Adult horse 2 = Young (< 6 months)
Then 1 indicates an adult horse, and since there are no 2s in the second column of the data or test files, I'd guess that 9 indicates a horse younger than 6 months. Let's check.
Column 2 contains only the values 1 and 9. In the data file, 24 of the 300 records have a value of 9 (8%), and in the test file, 4 of 68 records have a value of 9 (6%). Similar percentages is a good sign that 9 means a young horse (instead of 2).
The missing data, of which they claim there is 30%, is marked by a
? in other columns.
To get confirmation, feel free to contact the authors. And also consider reporting the bug to UCI.