The data I have contained some missing value for my numeric variable, and thus when I destring this variable, I also have an error.

And I use tab to find out the missing characteristic, and here is what I found:

unemployment |
_rate | Freq. Percent Cum.
-------------+-----------------------------------
- | 240 0.02 0.02
0.0 | 27 0.00 0.02
0.1 | 1 0.00 0.02
0.2 | 7 0.00 0.02
0.3 | 14 0.00 0.02
0.4 | 20 0.00 0.02
0.5 | 45 0.00 0.03

Anyone has an idea about the missing value (first row I showed)

I try "-"," -", and " -", and non of this work.