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Re: st: Looping over variables


From   Nick Cox <njcoxstata@gmail.com>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: Looping over variables
Date   Wed, 19 Dec 2012 12:46:05 +0000

Your results are correct. The problem was mine; precedence rules mean
that the code should have been

replace n_preg = n_preg + (inlist(aa`j', 1, 5) | (inlist(aa`j', 2, 3,
4, 6, 7) & inrange(aa`J', 13, .)))

to ensure that the entire logical condition is evaluated separately.
Sorry about that.

Nick

On Wed, Dec 19, 2012 at 12:30 PM, Ingeborg Forthun
<ingeborg.forthun@gmail.com> wrote:
> I am sorry if I have misunderstood, but the two codes do not give the
> same result.
>
> The first code:
> gen n_preg = 0
> forval j = 95(6)149 {
>         local J = `j' + 1
>         replace n_preg = n_preg + inlist(aa`j', 1, 5) | (inlist(aa`j', 2, 3,
>  4, 6, 7) & inrange(aa`J', 13, .))
>  }
>
> returns:
>
>    n_preg |      Freq.     Percent        Cum.
> ------------+-----------------------------------
>           0 |     46,703       45.91       45.91
>           1 |     55,024       54.09      100.00
> ------------+-----------------------------------
>       Total |    101,727      100.00
>
>
> The second code:
> gen n_preg = 0
> forval j = 95(6)149 {
>         local J = `j' + 1
>         replace n_preg = n_preg + 1 if inlist(aa`j', 1, 5) |
> (inlist(aa`j', 2, 3,
>  4, 6, 7) & inrange(aa`J', 13, .))
>  }
>
> returns:
>
>   n_preg |      Freq.     Percent        Cum.
> ------------+-----------------------------------
>           0 |     46,703       45.91       45.91
>           1 |     35,664       35.06       80.97
>           2 |     15,164       14.91       95.88
>           3 |      3,303        3.25       99.12
>           4 |        682        0.67       99.79
>           5 |        143        0.14       99.93
>           6 |         35        0.03       99.97
>           7 |         19        0.02       99.99
>           8 |          7        0.01       99.99
>           9 |          4        0.00      100.00
>          10 |          3        0.00      100.00
> ------------+-----------------------------------
>       Total |    101,727      100.00
>
>
> This is what I need to know. I have to know the exact number of
> pregnancies and not only 0 or 1.
>
> Ingeborg
>
> 2012/12/19 Nick Cox <njcoxstata@gmail.com>:
>> This is likely to be confusing to others.
>>
>> As you say, you want to count the number of pregnancies and my code,
>> along the lines suggested by Daniel, does that. It does that because
>> the logical condition evaluates to 1 or 0, which gives you the right
>> answer.
>>
>> In a simpler example if you are counting instances of 42 or 43 then
>>
>> inlist(42, 42, 43)
>>
>> returns 1 and
>>
>> inlist (24, 42, 43)
>>
>> returns 0  -- so in a loop you can use that result directly. You could
>> say something like
>>
>> replace n42_43 = n42_43 + inlist(<whatever>, 42, 43)
>>
>> You don't have to say
>>
>> replace n42_43 = n42_43 + 1 if inlist(<whatever>, 42, 43)
>>
>> If you want to write it your way, that's fine, but there is no sense
>> in which you _have_ to do that.
>>
>> Nick
>>
>> On Wed, Dec 19, 2012 at 9:56 AM, Ingeborg Forthun
>> <ingeborg.forthun@gmail.com> wrote:
>>> Thank you very much for your advice!  It works! But as I want to count
>>> the number of pregnancies for each observation (forgot to write this
>>> in my first e-mail!) I had to add +1 in the third line in order for it
>>> to add 1 for each pregnancy.
>>>
>>>  gen n_preg = 0
>>>
>>> . forval j = 95(6)149 {
>>>   2.         local J = `j' + 1
>>>   3.         replace n_preg = n_preg + 1 if inlist(aa`j', 1, 5) |
>>> (inlist(aa`j', 2, 3, 4, 6, 7) & inrange(aa`J', 13, .))
>>>   4. }
>>>
>>>
>>>  Ingeborg
>>>
>>>
>>> 2012/12/18 Nick Cox <njcoxstata@gmail.com>
>>>>
>>>> I agree with Daniel's main advice. You can simplify this (e.g.)
>>>>
>>>> gen n_preg = 0
>>>> forval j = 95(6)149 {
>>>>         local J = `j' + 1
>>>>         replace n_preg = n_preg + inlist(aa`j', 1, 5) | (inlist(aa`j', 2, 3,
>>>> 4, 6, 7) & inrange(aa`J', 13, .))
>>>> }
>>>>
>>>> See also for specific and general advice:
>>>>
>>>> [D]     functions . . . . . . . . . . . . . . .  inlist() programming function
>>>>         (help inlist())
>>>>
>>>> [D]     functions . . . . . . . . . . . . . . . inrange() programming function
>>>>         (help inrange())
>>>>
>>>> SJ-9-1  pr0046  . . . . . . . . . . . . . . . . . . .  Speaking Stata: Rowwise
>>>>         (help rowsort, rowranks if installed) . . . . . . . . . . .  N. J. Cox
>>>>         Q1/09   SJ 9(1):137--157
>>>>         shows how to exploit functions, egen functions, and Mata
>>>>         for working rowwise; rowsort and rowranks are introduced
>>>>
>>>> SJ-6-4  dm0026  . . . . . . Stata tip 39: In a list or out? In a range or out?
>>>>         . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  N. J. Cox
>>>>         Q4/06   SJ 6(4):593--595                                 (no commands)
>>>>         tip for use of inlist() and inrange()
>>>>
>>>> It seems also that the names of your variables bear little relation to
>>>> their contents. Systematic use of -rename- is likely to make further
>>>> analysis much easier (and less error-prone).
>>>>
>>>> Finally, for "STATA" read "Stata", and please read the Statalist FAQ
>>>> to see why.
>>>>
>>>> Nick
>>>>
>>>> On Tue, Dec 18, 2012 at 8:47 AM, daniel klein <klein.daniel.81@gmail.com> wrote:
>>>>
>>>> > You could probably create a loop over the values 95, 101 and so on,
>>>> > and add 1 to the respective number inside the loop to get at the
>>>> > durration. But I would look at -egen-'s -anycount()- function first.
>>>> > This might be a good way of approching this.
>>>>
>>>> Ingeborg Forthun
>>>>
>>>> > [...]
>>>> > I want to make a variable that counts the number of pregnancies for each
>>>> > woman if outcome is 1 or 5 or if outcome is 2,3,4,6 or 7 and number of
>>>> > weeks of pregnancy was more than 12 weeks. Number of weeks of
>>>> > pregnancy is given by aa96 (corresponding to the outcome of the first
>>>> > pregnancy given by aa95), aa102 (corresponding to the outcome of the
>>>> > second pregnancy given by aa101), and so on.
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