Hi all,

I am merging a number of different datasets and am having trouble with the merge command "deleting" cell values.

My starting panel dataset looks like this:
Code:
county year var1 var2
  1      1   25   30
  1      2   35   22
  1      3   40   50
  2      1   34   30
  2      2   45   44
  2      3   56   21
  3      1   23   12
I wish to merge it with a dataset that looks like this (i.e., adding two additional variables to the dataset):
Code:
county year var3 var4
  1      1   27   28
  1      2   34   32
  1      3   43   42
  2      1   32   33
  2      2   43   24
  2      3   67   23
However, when I use the merge command Stata "deletes" the original variables (var1 and var2) and turns them into missing values.

The dataset ends up looking like this:
Code:
county year var1 var2 var3 var4
  1      1   .    .   27   28
  1      2   .    .   34   32
  1      3   .    .   43   42
  2      1   .    .   32   33
  2      2   .    .   43   24
  2      3   .    .   67   23
Here's the basic code I'm using. Sometimes the problem doesn't occur for the first dataset I'm merging and then the deletion happens for the remaining datasets I'm attempting to merge.
Code:
merge m:1 county year using "X.dta"
Any help would be much appreciated. Thank you!
Matt