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From |
"Nick Cox" <n.j.cox@durham.ac.uk> |

To |
<statalist@hsphsun2.harvard.edu> |

Subject |
st: RE: Re: Collapse & Missing Values |

Date |
Wed, 28 Sep 2005 22:38:22 +0100 |

I think this needs a tweak: bysort date (sum): keep if _n == 1 will ensure that the first value of -sum- in each group after sorting is missing if and only if -sum- is missing on all values in each group. With the code as is stands you could lose sums you want to keep. Nick n.j.cox@durham.ac.uk Friedrich Huebler > 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" <ewruck@econalytics.com> 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? * * For searches and help try: * http://www.stata.com/support/faqs/res/findit.html * http://www.stata.com/support/statalist/faq * http://www.ats.ucla.edu/stat/stata/

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