Generate variable with odd and even labels - stata

Question

I have a variable num with values 1-10.
I would like to create a new variable type with values odd or even:
generate type = odd if inlist(num, 1,3,5,7,9)
Questions:
What is the cleanest way to also label even numbers?
Could I use a negation somewhere and keep the command all in one line?

Answer 1

The code you provide is not valid syntax:
clear
set obs 10
generate num = _n
generate type = odd if inlist(num, 1,3,5,7,9)
odd not found
r(111);
You could get what you want with:
generate type = "odd" if inlist(num, 1,3,5,7,9)
And you can do both at the same time using the cond() function:
generate type = cond(inlist(num, 1,3,5,7,9), "odd", "even")
However, having this variable as a string will be of limited value for later use.
You could subsequently use the encode command to create a new variable of numeric type:
encode type, generate(type2)
list
+--------------------+
| num type type2 |
|--------------------|
1. | 1 odd odd |
2. | 2 even even |
3. | 3 odd odd |
4. | 4 even even |
5. | 5 odd odd |
|--------------------|
6. | 6 even even |
7. | 7 odd odd |
8. | 8 even even |
9. | 9 odd odd |
10. | 10 even even |
+--------------------+
Although seemingly identical, type and type2 variables are indeed of a different type:
list, nolabel
+--------------------+
| num type type2 |
|--------------------|
1. | 1 odd 2 |
2. | 2 even 1 |
3. | 3 odd 2 |
4. | 4 even 1 |
5. | 5 odd 2 |
|--------------------|
6. | 6 even 1 |
7. | 7 odd 2 |
8. | 8 even 1 |
9. | 9 odd 2 |
10. | 10 even 1 |
+--------------------+
This is how you can do it with type being a numeric variable:
generate type = mod(num, 2)
list
+------------+
| num type |
|------------|
1. | 1 1 |
2. | 2 0 |
3. | 3 1 |
4. | 4 0 |
5. | 5 1 |
|------------|
6. | 6 0 |
7. | 7 1 |
8. | 8 0 |
9. | 9 1 |
10. | 10 0 |
+------------+
You then create the value label and attach it to the variable type:
label define numlab 0 "even" 1 "odd"
label values type numlab
list
+------------+
| num type |
|------------|
1. | 1 odd |
2. | 2 even |
3. | 3 odd |
4. | 4 even |
5. | 5 odd |
|------------|
6. | 6 even |
7. | 7 odd |
8. | 8 even |
9. | 9 odd |
10. | 10 even |
+------------+
If you only want the odd numbers labeled you can simply do:
label define numlab 1 "odd"
If you later change your mind and want to add a label for even numbers:
label define numlab 0 "even", add

Answer 2

When your command has been run, the value of type for the odd numbers is "odd" and the value for the even numbers is "", that is a missing string.
You could tag the even numbers using
replace type = "even" if type==""
I cannot think of a way to keep it all in one line, since you have to both generate the variable and fill in two different string values.
If you could use a numeric variable (I name it flag) as your type variable, you could try this:
gen flag = mod(num,2)
This will flag the odd numbers as 1 and the even numbers as 0. You could then create a label for the flag variable, if you need to display its values as "odd" and "even".