STATA 11 for Windows SAMPLE SESSION - Food Security Group ...

Stata 11 Sample Session Section 2 – Restructuring Data Files – Table Lookup & Aggregation
We noted earlier that key variables are required for any
merge. When you're joining two files which are at the
same data level, as we're about to do, it may not seem
important to include key variables, but it is. The key
variables determine which observations are to be
combined.
Note: You should never use Combine datasets without
Key Variables because without them you have no
guarantee that the program will combine the cases in the
manner that you wish.
The command will execute without any warnings or error
messages, but the results may be incorrect.
At this point, if you have not closed Stata, hh-file2.dta is
still the working file.
A very important point: Stata cannot merge two
datasets unless they are both sorted in the order of the key
variables. One way to check to see if Stata knows the file
is sorted is to use the Describe command. In the Results
window you can see at the end of the list of variables, the
words “sorted by” and the list of variables that the file is
sorted by. Because we created hh-file1.dta by collapsing
the file, it is already sorted by district, vil and hh. hhfile2.dta
was also created by collapsing the file so it is
also sorted by district, vil and hh. We are ready to merge
the two files.
1. Select Data then Combine datasets then Merge
Two datasets
The Merge - Merge dataset in memory with dataset on
disk dialog box will appear. The default type of merge is
one-to-one on key variables – this is the merge we want
to do.
2. We are doing a one to one on key variables – type
of merge, the default selection. For the Filename of
dataset on disk box, click on the Browse button.
Select the file hh-file1.dta and click on Open
3. In the Key variables (match variables) box,
select
district vil hh
These are the Key Variables
4. Click on the Options tab. Under this tab, you see
the box labeled Specify new name of variable to
mark result of merge The default name is
_merge. This variable received a code of 1 or 2 or
3 to describe what type of merge occurred. The
code definition is:
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