Re: st: First date

[Keniajin Wambui <kiangati@gmail.com>]

Thanks Nick.

On Thu, Jan 31, 2013 at 3:05 PM, Nick Cox <njcoxstata@gmail.com> wrote:
> I discussed the misconception that changing the format of a date or
> time or date-time recasts to a different basis
> in the latest Stata Journal. To convert a date from one unit to
> another, you need a conversion, not a format change.
>
> Nicholas J. Cox
> Stata tip 113: Changing a variable's format: What it does and does not mean
> The Stata Journal
> Volume 12 Number 4: pp. 761-764
>
> See also point 3 in this recent posting
>
> http://www.stata.com/statalist/archive/2013-01/msg00893.html
>
> Nick
>
> On Thu, Jan 31, 2013 at 11:55 AM, Nick Cox <njcoxstata@gmail.com> wrote:
>> To put it more simply: -ndate_added- looks like a daily date. You need
>> to convert that to a date-time in milliseconds before you can add it
>> to the time of day in milliseconds. The factor is 24 * 60 * 60 * 1000.
>>
>> Nick
>>
>> On Thu, Jan 31, 2013 at 11:53 AM, Nick Cox <njcoxstata@gmail.com> wrote:
>>> Date-times for dates and times around now are in trillions (10^12 or
>>> so) of milliseconds
>>>
>>> . di %14.0f clock("02-Sep-2012 10:30:14", "DMYhms")
>>>  1662201014000
>>>
>>> so something is wrong with your variable -ndate_added-, because the
>>> values you have are far too small.
>>>
>>> More generally, what you should be doing is to add
>>>
>>> date-time in milliseconds = date in milliseconds + time of day in milliseconds
>>>
>>> but I guess what you are doing is adding
>>>
>>> date-time in milliseconds = date in some other units + time in milliseconds
>>>
>>> which won't work.
>>>
>>> Note also that whatever display format you assigned to -ndate_added-
>>> is quite immaterial; it's the numeric values underneath that format
>>> that your calculation uses.
>>>
>>> Nick
>>>
>>> On Thu, Jan 31, 2013 at 11:31 AM, Keniajin Wambui <kiangati@gmail.com> wrote:
>>>> I am using stataIC 12.1 64bit on windows 7.
>>>> I am calculating the first date the values for a given serial number
>>>> given was entered
>>>> The data example is
>>>>
>>>> time_done    ndate_added    serialNumber    dfst
>>>> 8:01:50 PM    26-Feb-09    88358        72127954
>>>> 4:56:27 PM    27-Feb-09    88358        61004955
>>>> 12:30:27 PM    25-Mar-09    88358        45044981
>>>> 10:30:14 PM    02-Sep-12    88358        81033238
>>>>
>>>>
>>>> I am using the following code but its giving me (12:30:27 PM
>>>> 25-Mar-09    88358)  as the first data to be entered but according to
>>>> the data (8:01:50 PM    26-Feb-09    88358) was the first to be
>>>> entered.
>>>>
>>>>     gen double timefst=clock(time_done, "hms")
>>>>     replace timefst=clock(time_done, "hm") if timefst==.
>>>>     format timefst %tc
>>>>     format ndate_added %tc
>>>>     gen dfst=ndate_added + timefst
>>>>     egen double fdoadd = min(dfst), by(serialNumber)
>>>>
>>>> how can I solve the problem
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