I have a long table with chronological data over several variables. In some instances, the data are missing, replaced by `"NA"`.
Example: 

```
2003-W01,NA,NA,NA,NA,NA,NA,0,1,2,2,7.593746345,86.84550216,13.223286,4.245984537

```

I want to be able to do computations on the elements under condition that none are negative or unavalailable.

How can I do this?