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From |
"Nick Cox" <n.j.cox@durham.ac.uk> |

To |
<statalist@hsphsun2.harvard.edu> |

Subject |
st: RE: Are there any date with time of day functions? |

Date |
Wed, 14 Apr 2004 19:44:22 +0100 |

The short answer is there is no support for time of day functions in official Stata as such. There still is much scope for using user-written material and/or more general commands or functions. My best single piece of advice, although it's biased, is to look at -split-. The material below is extracted from a posting on 28 January 2003. As far as official or public domain stuff is concerned, I think it remains fairly up-to-date. ======================= A colleague here asked about what support there was in Stata for time of day. It is of course well known that Stata supports dates at various time scales down to daily dates, but many projects also include data specifying time of day. It seems that any problems which arise lie in the range from (a) date_and_time problems: that is, you have a daily date and a time of day and the two together specify _when_ something happened. Most demanding is when you want to hold daily date + time in hours, minutes, seconds exactly. to (b) time problems: sometimes, the daily date is irrelevant or secondary and you just want to focus on time of day alone. Some notes follow my signature which may be of interest. I would appreciate comments on errors or omissions. Time of day =========== This is a note on what I know to be available in Stata to handle time of day data. 1. -egen- functions in user-written package -egenmore- ====================================================== Installed (in up-to-date Stata 7 or in Stata 8) by typing . ssc inst egenmore or in Stata 6 by using -archinst- (STB-54). -egenmore- is a library of -egen- functions. The general syntax is thus for function fcn egen [type] newvar = fcn(stuff) [if exp] [in range] [, options] dhms(d h m s) [ , format(format) ] creates a date variable from Stata date variable or date d with a fractional part reflecting the number of hours, minutes and seconds past midnight. h can be a variable containing integers between 0 and 23 inclusive or a single integer in that range. m and s can be variables containing integers between 0 and 59 or single integer(s) in that range. Optionally a format, usually but not necessarily a date format, can be specified. The resulting variable, which is by default stored as a double, may be used in date and time arithmetic in which the time of day is taken into account. elap(time) [ , format(format) ] creates a string variable which contains the number of days, hours, minutes and seconds associated with an integer variable containing a number of elapsed seconds. Such a variable might be the result of date/time arithmetic, where a time interval between two timestamps has been expressed in terms of elapsed seconds. Leading zeroes are included in the hours, minutes, and seconds fields. Optionally, a format can be specified. elap2(time1 time2) [ , format(format) ] creates a string variable which contains the number of days, hours, minutes and seconds associated with a pair of time values, expressed as fractional days, where time1 is no greater than time2. Such time values may be generated by function dhms(). elap2() expresses the interval between these time values in readable form. Leading zeroes are included in the hours, minutes, and seconds fields. Optionally, a format can be specified. hmm(timevar) generates a string variable showing timevar, interpreted as indicating time in minutes, represented as hours and minutes in the form "[...h]h:mm". For example, times of 9, 90, 900 and 9000 minutes would be represented as "0:09","1:30", "15:00" and "150:00". The option round(#) rounds the result: round(1) rounds the time to the nearest minute. The option trim trims the result of leading zeros and colons, except that an isolated 0 is not trimmed. With trim "0:09" is trimmed to "9" and "0:00" is trimmed to "0". hmm() serves equally well for representing times in seconds in minutes and seconds in the form "[...m]m:ss". hmmss(timevar) generates a string variable showing timevar, interpreted as indicating time in seconds, represented as hours, minutes and seconds in the form "[...h:]mm:ss". For example, times of 9, 90, 900 and 9000 seconds would be represented as "00:09","01:30", "15:00" and "2:30:00". The option round(#) rounds the result: round(1) rounds the time to the nearest second. The option trim trims the result of leading zeros and colons, except that an isolated 0 is not trimmed. With trim "00:09" is trimmed to "9" and "00:00" is trimmed to "0". hms(h m s) [ , format(format) ] creates an elapsed time variable containing the number of seconds past midnight. h can be a variable containing integers between 0 and 23 inclusive or a single integer in that range. m and s can be variables containing integers between 0 and 59 or single integer(s) in that range. Optionally a format can be specified. minutes(strvar) [ , maxhour(#) ] returns time in minutes given a string variable containing a time in hours and minutes in the form "[..h]hh:mm". In particular, minutes are given as two digits between 00 and 59 and hours by default are given as two digits between 00 and 23. The maxhour() option may be used to change the (unreachable) limit: its default is 24. (Stata 8 required.) seconds(strvar) [ , maxhour(#) ] returns time in seconds given a string variable containing a time in hours, minutes and seconds in the form "[..h]hh:mm:ss". In particular, minutes and seconds are each given as two digits between 00 and 59 and hours by default are given as two digits between 00 and 23. The maxhour() option may be used to change the (unreachable) limit: its default is 24. (Stata 8 required.) tod(time) [ , format(format) ] creates a string variable which contains the number of hours, minutes and seconds associated with an integer in the range 0 to 86399, one less than the number of seconds in a day. Such a variable is produced by hms(), which see above. Leading zeroes are included in the hours, minutes, and seconds fields. Colons are used as separators. Optionally a format can be specified. Kit Baum (baum@bc.edu) is the author of dhms(), elap(), elap2(), hms() and tod(). The other functions were written by myself. Stata 6 required, except that minutes() and seconds() require Stata 8. 2. -fodstr-, -fod2str- and -mkfrac- =================================== Installed (in up-to-date Stata 7 or in Stata 8) by typing . ssc inst fodstr N.B. no help files. fodstr newvar oldvar extracts the fraction-of-a-day stored in Stata's date format and formats it in readable (hh:mm:ss) form. fod2str newvar oldvar creates the full formatted dd mmmm yyyy hh:mm:ss form. mkfrac newvar oldvar performs the inverse trasformation; given a string variable containing a date, it returns the fraction of a day involved (i.e. 1 Jan 1998 06:00:00 becomes 0.5000). William Gould (wgould@stata.com) is the author. Stata 5 required. 3. FAQ on getting nice time labels ================================== I wrote an FAQ on getting "nice" time labels on graphs which is being processed by Stata Corp. The advice does not apply in all detail to Stata 8 graphs. [NJC note: now posted at http://www.stata.com/support/faqs/graphics/nicetime.html] 4. -split- ========== -split- is official in Stata 8. Otherwise . ssc inst split installs an unofficial version requiring Stata 7. An example at [R] split and in the on-line help explains how to use it with hh:mm:ss times. Appendix: Summary of transformation functions ============================================= egen, dhms() d h m s => date + fractional part elap() s => "d:hh:mm:ss" elap2() time1 time2 => (time2 - time1) as "d:hh:mm:ss" hmm() m => "...h:mm" s => "...m:ss" hmmss() s => "...h:mm:ss" hms() h m s => s minutes() "hh:mm" => m seconds() "hh:mm:ss" => s tod() s => "hh:mm:ss" fodstr d with fraction => fraction as "hh:mm:ss" fod2str d with fraction => date and time as "d hh:mm:ss" mkfrac "d hh:mm:ss" => d with fraction ==================== Nick n.j.cox@durham.ac.uk Pauline Rogers > I have just been given a dataset which contains variables > which give the > current date and time i.e. 29.10.1998:15:04. > > I have just searched for any functions that deal with this > type of data > without success (apart from the date functions within Stata). > > I know I can pick out elements from the variables and then > manipulate them > myself but before I re-invent the wheel does anyone know of > any functions > that will help? I need to extract just the date or just the > time; calculate > intervals between two time points (which could be on > different days); etc. > etc. * * For searches and help try: * http://www.stata.com/support/faqs/res/findit.html * http://www.stata.com/support/statalist/faq * http://www.ats.ucla.edu/stat/stata/

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