Re: st: Counting Instances of a value within a group

["Austin Nichols" <austinnichols@gmail.com>]

bys ID: egen D1=total(Dose==1)

On 9/12/06, Rachel S <academicgirl@gmail.com> wrote:
> I'm trying to figure out how to count the number of instances of a
> value of a variable within a group.
>
> The relevant subset of my dataset looks like
>
> ID   Dose  Drug
> 11    1        A
> 11    2        B
> 12    2       A
> 12    .        B
> 13    1       A
> 13    1      B
>
> I'd like to add two variables, Dose1 and Dose2, which count the number
> of drugs for which a patient is taking a dose of 1 or 2, respectively.
>  Each of these two new variables should be constant across
> observations for a patient.
>
> Dose can contain the number 1,2, or 3 or a missing value.
>
> I used the commands:
>
> by ID: egen Dose1=count(Dose) if Dose==1
> by ID: egen Dose2=count(Dose) if Dose==2
>
> However, this generates the variables Dose1 and Dose2 only for those
> observations with the relevant dose.  That is, the "if" statement
> seems to be attached to the egen command rather than the count
> function.
>
> How can I fix this?
>
> Thanks,
> Rachel
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