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Re: st: Create Timeline based on Dates


From   Nick Cox <njcoxstata@gmail.com>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: Create Timeline based on Dates
Date   Fri, 26 Oct 2012 10:18:41 +0100

On weekends:

It seems that you have Mondays to Fridays only in your data, and you
want time to run in sequence so that Monday follows Friday.

The -dow()- function returns 1 to 5 for Mondays to Fridays. A bit of
messing around yields a mapping to sequential "dates" that omit
Saturdays and Sundays. (If you want another origin, you can just shift
it.)

Again, I need a sandpit.

clear
set obs 14
gen date = mdy(10, 20, 2012) + _n
format date %td
gen dow = dow(date)

. l

     +-----------------+
     |      date   dow |
     |-----------------|
  1. | 21oct2012     0 |
  2. | 22oct2012     1 |
  3. | 23oct2012     2 |
  4. | 24oct2012     3 |
  5. | 25oct2012     4 |
     |-----------------|
  6. | 26oct2012     5 |
  7. | 27oct2012     6 |
  8. | 28oct2012     0 |
  9. | 29oct2012     1 |
 10. | 30oct2012     2 |
     |-----------------|
 11. | 31oct2012     3 |
 12. | 01nov2012     4 |
 13. | 02nov2012     5 |
 14. | 03nov2012     6 |
     +-----------------+

gen seqdate = (5 * (date - dow(date) - 2) / 7) + dow(date)
replace seqdate = . if inlist(dow(date), 0, 6)

. l

     +---------------------------+
     |      date   dow   seqdate |
     |---------------------------|
  1. | 21oct2012     0         . |
  2. | 22oct2012     1     13776 |
  3. | 23oct2012     2     13777 |
  4. | 24oct2012     3     13778 |
  5. | 25oct2012     4     13779 |
     |---------------------------|
  6. | 26oct2012     5     13780 |
  7. | 27oct2012     6         . |
  8. | 28oct2012     0         . |
  9. | 29oct2012     1     13781 |
 10. | 30oct2012     2     13782 |
     |---------------------------|
 11. | 31oct2012     3     13783 |
 12. | 01nov2012     4     13784 |
 13. | 02nov2012     5     13785 |
 14. | 03nov2012     6         . |

If you are now going to tell me that the schools have
{holidays|vacations} too, then you really need a business calendar.


On Fri, Oct 26, 2012 at 9:36 AM, Nick Cox <njcoxstata@gmail.com> wrote:
> For problems like this I need a sandpit to play in. Here is one I made:
>
> list, sepby(id)
>
>      +-------------------+
>      | id   date   event |
>      |-------------------|
>   1. |  1     13       0 |
>   2. |  1     13       0 |
>   3. |  1     14       1 |
>   4. |  1     15       0 |
>   5. |  1     17       0 |
>   6. |  1     18       1 |
>   7. |  1     19       0 |
>      |-------------------|
>   8. |  2     14       0 |
>   9. |  2     15       0 |
>  10. |  2     15       1 |
>  11. |  2     17       0 |
>  12. |  2     18       0 |
>  13. |  2     19       1 |
>  14. |  2     20       0 |
>      +-------------------+
>
> I see this as follows.
>
> 1. There is a date looking forward, which is (present date - previous
> event date), and is thus zero or positive
>
> 1'. There is a twist on 1: There can be multiple observations with the
> same date.
>
> 2. There is a date looking backward which is (present date - next
> event date), and is thus zero or negative
>
> 2'. As 1'.
>
> 3. The wanted date is the smaller in absolute value. If there is a tie
> in absolute value, I choose the positive value.
>
> 4. For dates before the first event, no previous date can be
> identified. But this is not a problem, as the backward date will be
> the solution for these dates.
>
> 4. For dates after the last event, no next date can be identified. But
> this is not a problem, as the forward date will be the solution for
> these dates.
>
> To get "forward dates", we just copy previous values as needed, after
> spreading each event to all dates that are the same:
>
> gen prev = date if event == 1
> bysort id date (prev) : replace prev = prev[1] if prev[1] == 1
> bysort id (date) : replace prev = prev[_n-1] if mi(prev)
> gen forward = date - prev
>
> To get "backward dates", we can use the trick of reversing time.
>
> gen negdate = -date
> gen next = date if event == 1
> bysort id negdate (next) : replace next = next[1] if next[1] == 1
> bysort id (negdate) : replace next = next[_n-1] if mi(next)
> gen backward = date - next
>
> Now can we do the comparison:
> .
> gen timeline = cond(abs(forward) <= abs(backward), forward, backward)
> sort id date
>
> list id date forw backw timeline, sepby(id)
>
>      +-------------------------------------------+
>      | id   date   forward   backward   timeline |
>      |-------------------------------------------|
>   1. |  1     13         .         -1         -1 |
>   2. |  1     13         .         -1         -1 |
>   3. |  1     14         0          0          0 |
>   4. |  1     15         1         -3          1 |
>   5. |  1     17         3         -1         -1 |
>   6. |  1     18         0          0          0 |
>   7. |  1     19         1          .          1 |
>      |-------------------------------------------|
>   8. |  2     14         .         -1         -1 |
>   9. |  2     15         0          0          0 |
>  10. |  2     15         0          0          0 |
>  11. |  2     17         2         -2          2 |
>  12. |  2     18         3         -1         -1 |
>  13. |  2     19         0          0          0 |
>  14. |  2     20         1          .          1 |
>      +-------------------------------------------+
>
> For the complication with weekends, Stata offers business calendars as
> a complete solution. I have never used them.
>
> On Fri, Oct 26, 2012 at 1:02 AM, Lisa Wang <lhwang0925@gmail.com> wrote:
>
>> I would like to create a timeline based on some event date (ie. ...-5,
>> -4, -3, -2, -1, 0, +1, +2, +3...etc). I have different students names
>> in a variable named "as" (column 1)  and also a set of dates (column
>> 2) as well as another variable 'edate' (column 3) which has the event
>> dates and . everywhere else if it didn't match with column 2. What I
>> would like to know is how to create the timeline with the event date
>> being 0 for each student.
>>
>> This is the code I have run so far:
>>
>> - bysort as: generate rank =_n
>>
>> . bysort as: generate erank = rank if date==edate
>>
>> . bysort as: egen erank_pop = min(erank)
>>
>> . bysort as: generate t = rank -erank_pop -
>>
>> There are three problems which have me now stuck.
>>
>> 1. I might have multiple observations for a particular student on the
>> same date as well. Therefore, when I run the first line of code, it's
>> already erroneous as Stata will treat it as being different dates. I
>> tried also -bysort as(date): generate rank =_n - instead but it
>> returns an error: "factor variables and time-series operators not
>> allowed".
>>
>> 2. Sometimes I have multiple event dates for a particular student - I
>> would like Stata to guess which event date the date is closer to and
>> then do the time differences from that.
>>
>> 3. The dates in column 2 have all weekdays but no weekends (as the
>> students don't need to go to school on those days), so if I do a
>> timeline then it will skip some dates (eg. -5 then to -2,-1 etc. as a
>> result of the weekend). How would I overcome this, so that it actually
>> is -3,-2,-1 etc?
>>
>>
>> Thank you so much. My email is a bit long but just wanted everyone to
>> understand what I wanted to achieve.
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