I was envisioning a matrix with the rows equaling the number of zip codes and the columns equaling the number of dates.

That's what it does. From my earlier post,

CANDID       ZIP   MONEY (11062000)  MONEY (11072000)
C1234      12345                250                 0
C1234      33480                  0                 0
C1234      38401                  0                 0
C1234      67890                  0                 0
C1234      75711                  0                 0
C1234      77024                  0                 0
[download]

6 zips, so 6 rows.
2 dates, so 2 cols.

Note that 250 is the sum of two different amounts.

Instead what I get is a matrix 4000 X 4000

Not using my code, you didn't. As for the problem with your code, I don't know what you're expecting from me without showing me the code.