Dropping columns/variables based on count of missing in Stata -

i have large dataset looks 1 below. drop variables (not observations/rows) have less 3 observations in rows. in case variable x1 needs dropped.

i apologise if asking obvious, however, @ point not have clue on how proceed this.

+-----+-----+-----+-----+-----+ | id  |  x1 | x2  | x3  | x4  | +-----+-----+-----+-----+-----+ |  1  |  .  |  1  |  1  |  2  |     |  2  |  .  |  2  |  2  |  3  |     |  3  |  .  |  3  |  1  |  .  |    |  4  |  1  |  .  |  3  |  1  |    |  5  |  .  |  2  |  4  |  3  |    |  6  |  2  |  3  |  .  |  .  |     |total|  2  |  5  |  5  |  4  |    +-----+-----+-----+-----+-----+ 

my interpretation want drop variables have @ least 3 missing values.

you can use nmissing, ssc (ssc install nmissing):

clear set more off  input /// x y z . . 5 . 6 8 4 . 9 . . 1 5 . . end  list  nmissing, min(3) drop `r(varlist)' 

if interpretation incorrect, check help nmissing , npresent. syntax flexible enough.

edit

a re-interpretation. want drop variables don't have @ least 3 non-missing values:

clear set more off  input /// id    x1  x2   x3   x4   1    .    1    1    2       2    .    2    2    3       3    .    3    1    .      4    1    .    3    1      5    .    2    4    3      6    2    3    .    .    end  list, sep(0)  npresent, min(3) keep `r(varlist)'  describe