Thank you Nick. This is indeed the case. I'll have another look at it
when I get back from work. Maybe if I instead code the time according
to date in addition I'd get the correct elapsed time ? ie I add
another day to the measurements after midnight.
M
On Tue, Dec 22, 2009 at 12:48 PM, Nick Cox <[email protected]> wrote:
> As I understand it, you have subtracted one date-time from another, but the result is not itself a date-time. It is an elapsed time, and Stata lacks any support specific to elapsed times. So, for example, 1 (elapsed) day and 2 (elapsed) days look identical in terms of clock time, as you already know.
>
> . di %tc_HH:MM:SS 24 * 60 * 60 * 1000
> 00:00:00
>
> . di %tc_HH:MM:SS 48 * 60 * 60 * 1000
> 00:00:00
>
> Conversely, the difference between 21 December 2009 and 22 December 2009 is not as indicated by
>
> . di %d mdy(12,22,2009) - mdy(12,21,2009)
> 02jan1960
>
> But just 1 day.
>
> In short, applying date-time formats to elapsed times at best tells only part of the story and at worst gives you nonsense. That shouldn't be a surprise when you think about it.
>
> For elapsed times, you need to create your own code (setting aside earlier user-written efforts best consigned to history).
>
> In essence, Stata carries no knowledge forward of how your variables were calculated. As I guessed earlier in the thread, you assigned a format that is no use for graphing, as it does not distinguish elapsed times except in terms of what a clock would show.
>
> I asked earlier for you to -summarize- the values of your variables, but I've not seen any results. From your graph it seems that the data fall into two distinct subsets, times less than 1 day and times more than 1 day. I can't suggest why that is, but only looking at your data closely can tell you if there is some error or this does in fact make sense.
>
> As I suggested earlier, it is likely that you need to create your own axis labels, using a conversion from milliseconds to hours. -mylabels- from SSC is there to help.
>
> Nick
> [email protected]
>
> moleps islon
>
> The measurements have taken place at -clock-. However trying to twoway
> graph with clock along the x axis resulted in the problem with
> changing dates and jumps on the graph. I tried to cricumvent this by
> subtracting clock with the first clock-value.. but as you see it
> leaves me with the same problem. I´m sure there is someway around
> this...
>
>
>
> .format x %9.0g
>
> . l x clock in 1/5
>
> +------------------+
> | x clock |
> |------------------|
> 1. | 0 18:46:46 |
> 2. | 18000 18:47:04 |
> 3. | 30000 18:47:16 |
> 4. | 36000 18:47:22 |
> 5. | 66000 18:47:52 |
> +------------------+
>
> M
>
>
>
>
> On Mon, Dec 21, 2009 at 9:58 PM, Martin Weiss <[email protected]> wrote:
>>
>> <>
>>
>> I am not sure why you - format x %td_HH:MM:SS- while I formatted - format x
>> %tc_HH:MM:SS-. What happens when you
>>
>> ***
>> format x %9.0g
>> l in 1/5
>> ***
>>
>>
>> HTH
>> Martin
>>
>>
>> -----Original Message-----
>> From: [email protected]
>> [mailto:[email protected]] On Behalf Of moleps
>> Sent: Montag, 21. Dezember 2009 21:51
>> To: [email protected]
>> Subject: Re: AW: st: RE: Graphing time on the x axis
>>
>> To me there doesnt seem to be any difference between the sets, but doing the
>> following explains why the graph looks as it does. However I do not
>> understand how this comes about or how I can rectify it...
>>
>>
>>
>> . list x in 1/5
>>
>> +----------+
>> | x |
>> |----------|
>> 1. | 00:00:00 |
>> 2. | 00:00:18 |
>> 3. | 00:00:30 |
>> 4. | 00:00:36 |
>> 5. | 00:01:06 |
>> +----------+
>>
>> . sort x
>>
>> . list x in 1/5
>>
>> +----------+
>> | x |
>> |----------|
>> 1. | 05:10:24 |
>> 2. | 05:10:30 |
>> 3. | 05:10:36 |
>> 4. | 05:10:42 |
>> 5. | 05:10:48 |
>> +----------+
>>
>>
>> M
>>
>>
>>
>> On 21. des. 2009, at 21.18, Martin Weiss wrote:
>>
>>>
>>> <>
>>>
>>> How is your dataset different from the one I am playing with?
>>>
>>>
>>> *******
>>> clear*
>>> set obs 1000
>>> set seed 10234
>>>
>>> gen x=(_n-1)*6000
>>>
>>> format x %tc_HH:MM:SS
>>>
>>> gen mean_amp =rnormal()
>>> gen meanp =rnormal()
>>>
>>> gen byte c7=(runiform()<.2)+1
>>>
>>> compress
>>>
>>> tw (line mean_amp x if c7==1) /*
>>> */ (line mean_amp x if c7==2) /*
>>> */ (line meanp x if c7==1) /*
>>> */ (line meanp x if c7==2)
>>> *******
>>>
>>>
>>> HTH
>>> Martin
>>>
>>> -----Original Message-----
>>> From: [email protected]
>>> [mailto:[email protected]] On Behalf Of moleps
>>> Sent: Montag, 21. Dezember 2009 20:32
>>> To: [email protected]
>>> Subject: Re: AW: st: RE: Graphing time on the x axis
>>>
>>> picture of the graph
>>>
>>> http://www.flickr.com/photos/45805518@N04/?saved=1
>>>
>>> commands
>>>
>>>
>>>
>>>
>>>
>>> . format x %td_HH:MM:SS
>>>
>>> . list x in 1/5
>>>
>>> +----------+
>>> | x |
>>> |----------|
>>> 1. | 00:00:00 |
>>> 2. | 00:00:18 |
>>> 3. | 00:00:30 |
>>> 4. | 00:00:36 |
>>> 5. | 00:01:06 |
>>> +----------+
>>> . tw (line mean_amp x if c7==1) (line mean_amp x if c7==2) (line meanp
>> x
>>> if c7==1) (line meanp x
>>>> if c7==2)
>>>
>>> Regards,
>>>
>>> M
>>>
>>>
>>>
>>> On 21. des. 2009, at 19.57, Martin Weiss wrote:
>>>
>>>>
>>>> <>
>>>>
>>>>
>>>> You should probably reproduce the problem with a dataset shipped with
>>> Stata.
>>>> Is the time variable numeric or string?
>>>>
>>>>
>>>>
>>>> HTH
>>>> Martin
>>>>
>>>>
>>>> -----Ursprüngliche Nachricht-----
>>>> Von: [email protected]
>>>> [mailto:[email protected]] Im Auftrag von moleps
>>>> Gesendet: Montag, 21. Dezember 2009 19:48
>>>> An: [email protected]
>>>> Betreff: Re: st: RE: Graphing time on the x axis
>>>>
>>>> Maybe I was unclear in my description of the graph, but i dont think it
>> is
>>> a
>>>> scale or label question. The problem is that given the coordinates
>> (00:00,
>>>> 2.3) (05:36,1.9) (07:20,3.1) (18:58,2.9) they are not graphed in that
>>> order;
>>>> Instead I have (07:20,3.1) (18:58,2.9) (00:00, 2.3) (05:36,1.9) ...
>>>>
>>>> Regards
>>>>
>>>> M
>>>>
>>>>
>>>> On 21. des. 2009, at 13.45, Nick Cox wrote:
>>>>
>>>>> Clearly you need to specify your own.
>>>>>
>>>>> A convenience tool is -mylabels- from SSC. You just need to specify the
>>>> conversion from Stata's underlying scale, presumably milliseconds, to
>> your
>>>> desired scale, which may be hours (you don't say what you want instead).
>>> See
>>>> the help for more.
>>>>>
>>>>> Nick
>>>>> [email protected]
>>>>>
>>>>> moleps islon
>>>>>
>>>>> I´ve created a variable, time, for two measurements that both have
>>>>> been subtracted from the starting time of the measuerement so that the
>>>>> two start out with time 00:00:00 and I have measurements every 10
>>>>> sec. However after doing a twoway plot the starting point is not
>>>>> 00:00:00. Instead I have these tick marks and values along the x
>>>>> axis:: 07:20--12:53--18:58--00:00--05:36.... Any ideas?
>
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>
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