Replace string value with a missing value (dot)

[Ana Vasconcelos]

I have a dataset with a variable "sex". I would like to know how can I replace a string value "missing" with a missing value (dot). Can you help me with the code?
I send an example of the dataset below. Thank. you very much

* Example generated by -dataex-. For more info, type help dataex
clear
input byte(sex nchresp nch415resp)
1 0 0
1 0 0
2 0 0
1 0 0
2 2 2
2 1 1
1 0 0
2 0 0
2 0 0
2 0 0
2 2 1
2 0 0
1 0 0
1 2 1
1 0 0
2 2 2
2 0 0
2 0 0
2 2 2
2 2 2
1 1 0
2 0 0
1 0 0
1 0 0
2 0 0
2 0 0
2 0 0
1 0 0
2 0 0
2 0 0
2 2 1
2 3 3
1 0 0
1 0 0
2 0 0
2 2 2
2 0 0
1 0 0
1 0 0
2 1 1
1 0 0
1 0 0
2 0 0
1 0 0
2 1 1
2 3 1
1 0 0
2 0 0
1 0 0
2 0 0
2 0 0
1 0 0
2 1 0
2 1 0
1 0 0
1 0 0
1 0 0
2 1 1
1 0 0
2 1 0
2 0 0
2 1 1
1 0 0
2 0 0
2 0 0
1 0 0
1 0 0
2 0 0
2 0 0
2 0 0
2 0 0
2 1 1
1 0 0
2 0 0
1 0 0
1 0 0
2 0 0
1 0 0
2 0 0
2 0 0
1 0 0
2 0 0
1 0 0
2 0 0
2 3 3
1 0 0
2 0 0
1 0 0
2 1 1
1 0 0
2 0 0
2 2 0
2 2 1
1 0 0
2 1 1
2 0 0
2 2 2
2 0 0
1 0 0
2 0 0
end
label values sex c_sex
label def c_sex 1 "male", modify
label def c_sex 2 "female", modify
label values nchresp c_nchresp
label values nch415resp c_nch415resp

[Clyde Schechter]

In the example data you show, sex is already a numeric variable. It has no missing values, and if it did, they would not appear as "missing," unless you specifically created a value label to do that. Perhaps this data is not from the data set you are looking for help with? Or perhaps it already is a value-labeled numeric variable in which some extended missing value is labeled as "missing," but you do not show any such observations in the example.

For a more helpful response, please post a data example that illustrates the problem you wish to solve. The data you show exhibits no problem resembling what you have asked about.