Faster way to convert a string array of dates to julian dates - Idl-pvwave

On Sep 24, 7:49 am, "Ryan." <rchug...@gmail.com> wrote:
> Hi All,
>
> I want to convert an string array of dates to julian numbers in the
> most efficient way in IDL. The only way I can come up with doing it
> is using a FOR loop but I'm hoping that some of you could help me to
> utilize IDL's super-duper array manipulation strengths. This is what
> I have:
>
> date format: YYYY-MM-DD HH:MM:SS.FFFF+TT
> F->fractions of a second
> T->time zone specification (e.g. -05 for Eastern Standard Time, etc.)
>
> I don't care much about the time zone because all the dates are given
> in UTC. It doesn't need to be included in the conversion.
>
> Given a string array like this:> dates = ['2007-09-21 12:15:00.0000+00', '2007-09-22 23:25:15.9999+00', ...]
>
> I can convert it using this code:
>
> juls = DBLARR(N_ELEMENTS(dates))
> FOR i=0, N_ELEMENTS(dates)-1 DO BEGIN
> splitdate = STRSPLIT(dates[i], ': +-', /EXTRACT)
> juls[i] = JULDAY(splitdate[1], splitdate[2], splitdate[0],
> splitdate[3], splitdate[4], splitdate[5])
> ENDFOR
>
> This works, but would like to know a more efficient way of converting
> it because I do this quite often.
>
> Thanks,
> Ryan.

If the format of your input strings are never changing (which you're
pretty much implicitly assuming with strsplit anyway), then:
juls = julday(strmid(dates,0,4),strmid(dates,5,2),strmid(dates,
8,2),strmid(dates,11,2),strmid(dates,14,2),strmid(dates,17,7))

On 24 sep, 14:49, "Ryan." <rchug...@gmail.com> wrote:
> Hi All,
>
> I want to convert an string array of dates to julian numbers in the
> most efficient way in IDL. The only way I can come up with doing it
> is using a FOR loop but I'm hoping that some of you could help me to
> utilize IDL's super-duper array manipulation strengths. This is what
> I have:
>
> date format: YYYY-MM-DD HH:MM:SS.FFFF+TT
> F->fractions of a second
> T->time zone specification (e.g. -05 for Eastern Standard Time, etc.)
>
> I don't care much about the time zone because all the dates are given
> in UTC. It doesn't need to be included in the conversion.
>
> Given a string array like this:> dates = ['2007-09-21 12:15:00.0000+00', '2007-09-22 23:25:15.9999+00', ...]
>
> I can convert it using this code:
>
> juls = DBLARR(N_ELEMENTS(dates))
> FOR i=0, N_ELEMENTS(dates)-1 DO BEGIN
> splitdate = STRSPLIT(dates[i], ': +-', /EXTRACT)
> juls[i] = JULDAY(splitdate[1], splitdate[2], splitdate[0],
> splitdate[3], splitdate[4], splitdate[5])
> ENDFOR
>
> This works, but would like to know a more efficient way of converting
> it because I do this quite often.
>
> Thanks,
> Ryan.

Hello,

you may want to explore the possibilities of c() format.
Unfortunately, as far as I know, it cannot deal with time zones yet.

The following lines would do the job avoiding FOR loops:

fmt='(C(CYI4,1X,CMOI2,1X,CDI2,1X,CHI2,1X,CMI2,1X,CSF7.4))'
juls=DBLARR(N_ELEMENTS(dates))
READS,dates,juls,FORMAT=fmt
tz=LONG(STRMID(dates,24))
juls=juls-tz/24.


Pedro

On Sep 24, 8:10 am, henryg...@gmail.com wrote:
> On Sep 24, 7:49 am, "Ryan." <rchug...@gmail.com> wrote:
>
>
>
> > Hi All,
>
> > I want to convert an string array of dates to julian numbers in the
> > most efficient way in IDL. The only way I can come up with doing it
> > is using a FOR loop but I'm hoping that some of you could help me to
> > utilize IDL's super-duper array manipulation strengths. This is what
> > I have:
>
> > date format: YYYY-MM-DD HH:MM:SS.FFFF+TT
> > F->fractions of a second
> > T->time zone specification (e.g. -05 for Eastern Standard Time, etc.)
>
> > I don't care much about the time zone because all the dates are given
> > in UTC. It doesn't need to be included in the conversion.
>
> > Given a string array like this:> dates = ['2007-09-21 12:15:00.0000+00', '2007-09-22 23:25:15.9999+00', ...]
>
> > I can convert it using this code:
>
> > juls = DBLARR(N_ELEMENTS(dates))
> > FOR i=0, N_ELEMENTS(dates)-1 DO BEGIN
> > splitdate = STRSPLIT(dates[i], ': +-', /EXTRACT)
> > juls[i] = JULDAY(splitdate[1], splitdate[2], splitdate[0],
> > splitdate[3], splitdate[4], splitdate[5])
> > ENDFOR
>
> > This works, but would like to know a more efficient way of converting
> > it because I do this quite often.
>
> > Thanks,
> > Ryan.
>
> If the format of your input strings are never changing (which you're
> pretty much implicitly assuming with strsplit anyway), then:
> juls = julday(strmid(dates,0,4),strmid(dates,5,2),strmid(dates,
> 8,2),strmid(dates,11,2),strmid(dates,14,2),strmid(dates,17,7))

WHOOPS! I didn't read the IDL help entry for julday closely enough.
For some reason they do Month, Day, Year, Hour, Minute, Second.
(Which makes little sense to me. I just assumed it was Year, Month,
Day....)