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From |
Michael Norman Mitchell <Michael.Norman.Mitchell@gmail.com> |

To |
statalist@hsphsun2.harvard.edu |

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

Date |
Tue, 11 May 2010 09:09:22 -0700 |

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 5960 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 8283 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 5960 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 8283 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 5960 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 8283 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 5960 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 8283 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?* * For searches and help try: * http://www.stata.com/help.cgi?search * http://www.stata.com/support/statalist/faq * http://www.ats.ucla.edu/stat/stata/

* * For searches and help try: * http://www.stata.com/help.cgi?search * http://www.stata.com/support/statalist/faq * http://www.ats.ucla.edu/stat/stata/

**References**:**st: How can I put the numerical values of a variable into a numlist?***From:*A Loumiotis <antonis.loumiotis@gmail.com>

**Re: st: How can I put the numerical values of a variable into a numlist?***From:*Michael Norman Mitchell <Michael.Norman.Mitchell@gmail.com>

**RE: st: How can I put the numerical values of a variable into a numlist?***From:*"Nick Cox" <n.j.cox@durham.ac.uk>

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