Eric,
Here is one way to preserve the missing value.
. bysort date: egen sum = sum(amount)
. replace sum = . if amount==.
(2 real changes made, 2 to missing)
. bysort date: keep if _n==1
(3 observations deleted)
. drop amount
. rename sum amount
. clist, noobs
date amount
10-Oct-1990 189
11-Oct-1990 .
12-Oct-1990 107
Friedrich Huebler
--- "Eric G. Wruck" <[email protected]> wrote:
> I just learned, rather inconveniently, that collapse doesn't work
> the
> way I'd like when encountering missing values. Here's an example:
> . l
>
> +----------------------+
> | date amount |
> |----------------------|
> 1. | 10-Oct-1990 200 |
> 2. | 10-Oct-1990 -75 |
> 3. | 10-Oct-1990 64 |
> 4. | 11-Oct-1990 . |
> 5. | 12-Oct-1990 107 |
> |----------------------|
> 6. | 12-Oct-1990 . |
> +----------------------+
>
> . collapse (sum) net_amt=amount, by(date)
>
> . l
>
> +-----------------------+
> | date net_amt |
> |-----------------------|
> 1. | 10-Oct-1990 189 |
> 2. | 11-Oct-1990 0 |
> 3. | 12-Oct-1990 107 |
> +-----------------------+
>
> .
> The problem is for the single 11-Oct-1990 observation. After
> collapsing, the missing value becomes a zero; in this instance I
> would have preferred it remain missing. The 12-Oct-1990 treatment
> is
> fine & what I expected. I suppose I could delete observations
> before
> performing the collapse but it would be better if there was some
> other option. Is there?
>
>
> Grazie,
>
>
> Eric
>
> --
>
> ===================================================
>
> Eric G. Wruck
> Econalytics
> 2535 Sherwood Road
> Columbus, OH 43209
>
> ph: 614.231.5034
> cell: 614.330.8846
> eFax: 614.573.6639
> eMail: [email protected]
> website: http://www.econalytics.com
>
> ====================================================
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