how to record properties of other variables in stata - for-loop

Question

I have to generate variables entry_1, entry_2 and entry_3 which will adopt the value 1 if id_i for that particular month had entry=1.
Example.
id month entry entry_1 entry_2 entry_3
1 1 1 1 0 0
1 2 0 0 0 0
1 3 0 0 1 1
1 4 0 0 0 0
2 1 0 1 0 0
2 2 0 0 0 0
2 3 1 0 1 1
2 4 0 0 0 0
3 1 0 1 0 0
3 2 0 0 0 0
3 3 1 0 1 1
3 4 0 0 0 0
Would anyone be so kind to propose an idea of how to implement a loop in order to do this?
I am thinking of something like this:
forvalues i=1(1)3 {
gen entry`i'=0
replace entry`i'=1 if on that particular month id=`i' had entry=1
}

Answer 1

You could do something like this (although your data don't quite look right for the question you're asking):
forvalues i = 1/3 {
gen entry_`i' = id == `i' & entry == 1
}
This generates a dummy variable entry_i for each i in the forvalues loop where entry_i = 1 if id is i and entry is 1, and 0 otherwise.

Answer 2

The code can be simplified down to at most one loop.
clear
input id month entry entry_1 entry_2 entry_3
1 1 1 1 0 0
1 2 0 0 0 0
1 3 0 0 1 1
1 4 0 0 0 0
2 1 0 1 0 0
2 2 0 0 0 0
2 3 1 0 1 1
2 4 0 0 0 0
3 1 0 1 0 0
3 2 0 0 0 0
3 3 1 0 1 1
3 4 0 0 0 0
end
forval j = 1/4 {
egen entry`j' = total(entry & id == `j'), by(month)
}
list id month entry entry? , sepby(id)
+--------------------------------------------------------+
| id month entry entry1 entry2 entry3 entry4 |
|--------------------------------------------------------|
1. | 1 1 1 1 0 0 0 |
2. | 1 2 0 0 0 0 0 |
3. | 1 3 0 0 1 1 0 |
4. | 1 4 0 0 0 0 0 |
|--------------------------------------------------------|
5. | 2 1 0 1 0 0 0 |
6. | 2 2 0 0 0 0 0 |
7. | 2 3 1 0 1 1 0 |
8. | 2 4 0 0 0 0 0 |
|--------------------------------------------------------|
9. | 3 1 0 1 0 0 0 |
10. | 3 2 0 0 0 0 0 |
11. | 3 3 1 0 1 1 0 |
12. | 3 4 0 0 0 0 0 |
+--------------------------------------------------------+