number of types within groups

[ching wong]

Hi

I have the following dataset.

ClientID Nurses
1 A
1 B
1 A
2 A
2 A
3 C
3 A
3 A

Now, I will need to find the number of nurses for each client during their episode of care. Therefore, I would like to see the following.

ClientID Nurses n_nurses
1 A 2
1 B 2
1 A 2
2 A 1
2 A 1
3 C 2
3 A 2
3 A 2


What command should I use.

I tried
sort ClientID Nurses
by ClientID Nurses: gen n_nurses=_n

But it doesn't work.

Thanks in advance.

[Carlo Lazzaro]

Ching:
I'm not clear with the meaning of "A", "B" and "C" in your example (by the way: please use -dataex-. Thanks).

[eric_a_booth]

Change your code:

by ClientID Nurses: gen n_nurses=_n

to

by ClientID Nurses: gen n_nurses=_N

but this wont match your second data example precisely (I think those are just errors), it will produce:

| ClientID Nurses n_nurse |
|------------------------------|
| 1 A 2 |
| 1 A 2 |
| 1 B 1 |
| 2 A 2 |
| 2 A 2 |
|------------------------------|
| 3 A 2 |
| 3 A 2 |
| 3 C 1 |

[Nick Cox]

The question therefore is why you thought that would be right. Even using _N rather than _n won't give you what you want.

See https://www.statalist.org/forums/for...r-double-group for the same question asked last week and one reference and one solution.

This is another way to do it directly:

clear 
input ClientID str1 Nurses
1 A
1 B
1 A
2 A
2 A
3 C
3 A
3 A
end 

bysort ClientID (Nurses) : gen Counter = sum(Nurses != Nurses[_n-1]) 
by ClientID : replace Counter = Counter[_N] 

list, sepby(ClientID) 

     +-----------------------------+
     | ClientID   Nurses   Counter |
     |-----------------------------|
  1. |        1        A         2 |
  2. |        1        A         2 |
  3. |        1        B         2 |
     |-----------------------------|
  4. |        2        A         1 |
  5. |        2        A         1 |
     |-----------------------------|
  6. |        3        A         2 |
  7. |        3        A         2 |
  8. |        3        C         2 |
     +-----------------------------+