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Re: st: Re: Dealing with missing values


From   njcoxstata@gmail.com
To   "statalist@hsphsun2.harvard.edu" <statalist@hsphsun2.harvard.edu>
Subject   Re: st: Re: Dealing with missing values
Date   Tue, 2 Apr 2013 06:57:36 +0100

The function -date()- fed in this way yields a daily date, corresponding to 1 January in the year.in question. It is difficult to imagine why you want that when your dates are yearly.

Your new variable is numeric,, so string functions and operations no longer apply.

The function name -date()- can be explained: it was introduced when daily dates were the only kind of date which Stata supported as such. The undocumented synonym -daily()- is a better match for what it does.

Your problem seems to call for -destring-, not -date()-. 


Nick
njcoxstata@gmail.com

On 2 Apr 2013, at 01:21, "Joseph Coveney" <stajc2@gmail.com> wrote:

> Ching Wong wrote:
> 
> I am currently using Stata 12.
> 
> I need to convert the variable 'year' to a numeric variable by using
> the commands, gen yr = date(year, "Y"). However, there is 1 missing
> value generated. I have no idea why it would happen. As I have checked
> every single obs for 'year', there is no missing value. But when I
> checked the obs for 'yr', there is one "." after converting from
> 'year' to 'yr'.
> 
> Why does it happen only for the year 1990 particularly, which is the
> maximum for the variable 'year'? And how should I deal with this
> missing value? I have tried to replace yr="" if yr==".". But it can't
> be eliminated. ie type mismatch r(109)
> 
> Year  Yr
> 1960   0
> 1940   -7305
> 1990   . <--??
> 1986   9497
> 1915   -16436
> 
> --------------------------------------------------------------------------------
> 
> Just a couple of suggestions.  Because Year is a string variable, it can take
> nonnumeric characters, some of which might not be readily discernable with some
> typefaces.  So, make sure that the one in the "1990" observation is a numeral
> and not a lower-case el, and that the zero is a zero and not an upper-case oh.
> Data-entry errors do happen.  You can scan for observations that aren't all
> numeric (that is, they contain at least one nonnumeric, nonwhite-space
> character) using the -real()- function, as in the line below.
> 
>    list Year if missing(real(Year))
> 
> If there's a single missing value in Yr and it's only for the year 1990, then
> you can replace it with the following.
> 
>   replace Yr = date("1990", "Y")
> 
> taking care when typing-in "1990".  It's a bit of a kludge, but you can think of
> it as a temporary workaround that will let you go on with your work while you
> figure out in parallel what's going wrong.
> 
> Joseph Coveney
> 
> P.S. It's always helpful to show exactly what you typed and exactly what you
> got, for example, a copy-and-paste from the Results window.  Sometimes you
> believe that you typed something that you didn't, and it's easier for others to
> see the problem when you copy-and-paste the Results screen verbatim rather than
> paraphrase as you did.
> 
> . input str4 Year
> 
>          Year
>  1. 1960
>  2. 1940
>  3. 1990
>  4. 1986
>  5. 1915
>  6. end
> 
> . 
> . generate float Yr = date(Year, "Y")
> 
> . list, noobs
> 
>  +---------------+
>  | Year       Yr |
>  |---------------|
>  | 1960        0 |
>  | 1940    -7305 |
>  | 1990    10958 |
>  | 1986     9497 |
>  | 1915   -16436 

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