Re: st: How can I put the numerical values of a variable into a numlist?

[Michael Norman Mitchell <Michael.Norman.Mitchell@gmail.com>]

Dear Nick

  Thanks for noting the limits of my answer! Indeed,

. levelsof id, local(a)

   is not only a more robust solution, but is is also simpler.

Thanks!

Michael N. Mitchell
See the Stata tidbit of the week at...
http://www.MichaelNormanMitchell.com

On 2010-05-11 4.31 AM, Nick Cox wrote:
> -levelsof- is the appropriate command. However, the way Michael uses it
> here leads to the right answer for very simple examples but otherwise
> could easily bite you by giving an incomplete answer. Consider this
> example:
>
> . clear
>
> . set obs 100
> obs was 0, now 100
>
> . gen id = _n
>
> . levelsof id
> 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27
> 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51
> 52 53 54 55 56 57 58 59
>    
> >   60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82
> >      
> 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100
>
> . local a = r(levels)
>
> . di "`a'"
> 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27
> 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51
> 52 53 54 55 56 57 58 59
>    
> >   60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82
> >      
> 83 84
>
> What happened to the list of identifiers? Why is it truncated?
>
> The use of the = sign implies an _evaluation_ of the following
> expression, here r(levels). But there is a limit on the length of the
> expression that Stata can handle. This is documented at [U] 18.3.4
> Macros and expressions and also in
>
> SJ-8-4  pr0045  . . . . . . . . Stata tip 70: Beware the evaluating
> equal sign
>          . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  N.
> J. Cox
>          Q4/08   SJ 8(4):586--587                                 (no
> commands)
>          tip explaining the pitfall of losing content in a macro
>          because of limits on the length of string expressions
>
> There are two better ways to proceed. The first is just to copy, as no
> evaluation is needed anyway:
>
> . local a `r(levels)'
>
> The second is use -levelsof-'s -local()- option.
>
> . levelsof id, local(a)
> 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27
> 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51
> 52 53 54 55 56 57 58 59
>    
> >   60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82
> >      
> 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100
>
> . di "`a'"
> 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27
> 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51
> 52 53 54 55 56 57 58 59
>    
> >   60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82
> >      
> 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100
>
> I'd always recommend this second way.
>
> Nick
> n.j.cox@durham.ac.uk
>
> Michael Norman Mitchell
>
>     Does this example help?
>
> . sysuse auto
> (1978 Automobile Data)
>
> . levelsof mpg
> 12 14 15 16 17 18 19 20 21 22 23 24 25 26 28 29 30 31 34 35 41
>
> . local a = r(levels)
>
> . di "`a'"
> 12 14 15 16 17 18 19 20 21 22 23 24 25 26 28 29 30 31 34 35 41
>
>
> On 2010-05-10 10.43 PM, A Loumiotis wrote:
>
>    
> > Is there any way to put the numerical values of a variable into a
> > numlist beside doing it manually?
> >      
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