My app lets people log the movies they see (for example). Each logged movie usually (but not always) has a date and sometimes has a time. It's not unusual to have one but not the other. Occasionally the dates are only a year ("I watched a Dumbo sometime in 1984"), but could realistically be any combination of day/month/year/time.
I am used to modeling dates as date objects in my app and my backend. But is it a viable approach to store each component separately? When I need to reference an actual date from the components (e.g. for sorting the log) this will be built client-side, or perhaps be stored as a derived property sortDate and updated whenever any of the components change.
My reservation is that the information the user is saving is truly a 'moment in time' and I will have to take care of some things myself - for example what time zone are my components stored relative to? This would be captured automatically as part of a real Date object.
The alternative seems to be assuming some sort of 'default' for missing components (e.g. year 0000 if no year, time 00:00 if no time). But those defaults have meaning and I won't be able to distinguish them from 'not provided'.
What are the limitations and/or pitfalls of this approach? Does anyone have experience modeling their dates this way?
If it's of any consequence, my app is for iOS written in Swift and uses a Parse Server backend.
I've successfully used question marks to represent ambiguous and unknown timestamp parts in legal systems. Try to keep in mind that you're really not modeling dates here ('1984' isn't a date); you're modeling facts about dates.
So, if one of your users saw a movie some time in 1984, you might record the value '1984-??-?? ??:??:??' in a text column in a database. Values like this sort sensibly.
See also this answer on dba. Comments on that answer are also good to read.
Can anyone shed light on the following dilemma, please?
I have the need for a custom formula that allows conditional formatting for any rows who's date in columnB is 3 weekdays AHEAD of today's current date.
For example, if today was Wednesday 12/3 then I need to format any rows who's colB date is 3 working days in the future Thus (Monday 12/8) would be formatted....skipping any weekend days. No other days before or after (Monday 12/8) would be formatted.
To explain the premise, Sales staff can view this page and know that all jobs due to be installed 3 days from today (highlighted, say in yellow) must be turned in for processing today. Thus the need to exclude all weekend days.
This forum has helped me so very much to accomplish my Production Schedule using Sheets, as I have zero experience. You guys have been the best and I am in hopes this too can be resolved.
For reference you can view the test data sheet named "DUE_AMBER" at the below link where all rows having date of "Mon, Dec 8" would be only rows impacted
https://docs.google.com/spreadsheets/d/1goG0TS1_2jwlGRetREYNRVk-Q6TEy3iWG_5VXFoZlus/edit?usp=sharing
Thanks.
Seems OP is happy enough with this answer of his own:
=(if(networkdays(TODAY(),(INDIRECT("B"&ROW())))=4,1,0))=1
So I am in charge of office hours for a class at my University. I have to send out a google form every week for the students to sign up. The way the form is sent back, the data is grouped by Name, and the times they are available are grouped by days.
To make it easier on myself, I want to group it by times. Basically, I want it so that each day/time will have its own row, and the names of the people who want the time slot would be grouped together in the adjacent column.
I already separated the groups of times so that each time has its own cell, but I cannot figure out how to regroup the data by time.
I should also mention that each session of OH is 30 minutes and that each student can only receive one session of office hours a week because of limited availability. I also need to group the sessions into blocks so that the teachers won't have idle time (basically a teacher will have office hours from 5:00-6:30 PM on Tuesday, instead of 5:00-5:30 PM and 6:00-6:30 PM on Tuesday and 8:00-8:30 PM on Thursday). Grouping the names of the people who want office hours by the times that they are available would make it a lot easier to set up that week's office hours schedule.
Here's a link to an example:
https://docs.google.com/spreadsheets/d/1fRYYNUoEcgynU9cDMoXzsyjtIir4hsRlfFYJau36a78/edit?usp=sharing
have a look at this sheet ( i have only turned on sharing temporarily, co copy this to your own drive)
Look at the "matrix choices" sheet.
I created a Matrix of students and times (which I think is better), but there is also a list of names for each timeslot on the end too.
have a play changing some of the 1's (sessions applied for) to "G" (short for Granted). Ive set up some conditional formatting and data validation.
I have a requirement to store dates and durations arising from multiple different calendars. In particular I need to store dates that:
Span the change to Gregorian calendars in different countries at different times
Cover a historic period of at least 500 years
Deal with multiple types of calendar - lunar, solar, Chinese, Financial, Christian, UTC, Muslim.
Deal with the change, in the UK, of the year end from 31st March to 31st December, and comparable changes in other countries.
I also need to store durations which I have defined as the difference between two timestamps (date and time). This implies the need to be able to store a "zero" date - so I can store durations of, say, three and a half hours; or 10 minutes.
I have details of the computations needed. Firebird's timestamp is based on a date function that starts at January 1st, 100 CE, so is not capable of being used for durations in the way I need to record them. In addition this data type is geared up (like most timestamp functions) to record the number of days since a base date; it is not geared up to record calendar dates.
Could anyone suggest:
A data structure to store dates and durations that meet the above requirements OR
A reference to such a data structure OR
Offer guidelines to approach the structuring of such storage OR
Any points that may help me to a solution.
EDIT:
#Warren P has provided some excellent work in his responses. I obviously have not explained what I am seeking clearly enough, as his work concentrates on the computations and how to go about calculating these. All valuable and useful stuff, but not what I intended my question to convey.
I do have details of all the computations needed to convert between various representations of dates, and I have a fairly good idea of how to implement them (using elements such as Warren suggests). However, my requirement is to STORE dates which meet the various criteria listed above. Example: date to be stored - 'Third June 13 Charles II'. I am trying to determine an appropriate structure within which to store such dates.
EDIT:
I have amended my proposed schema. I have listed the attributes on each table, and defined the tables and attributes by examples, given in the third section of the entity box. I have used the example given in this question and answer in my definition by example, and have amended the example in my question to correspond. Although I have proved my schema by describing somebody else's example, this schema may still be over complicated; over analysed; miss some obvious simplification and may prove very difficult to implement (Indeed, it may be plain wrong). Any comments or suggestions would be most welcome.
If you are writing your own, as I assume you intend to, I would make a class that contains a TDateTime, and other fields, and I would base it on the functionality in the very nicely written mxDateTime extension for Python, which is very easily readable, open source, C code, that you could use to extract the gregorian calendar logic you are going to need.
Within certain limits, TDateTime is always right. It's epoch value (0) is December 30, 1899 at midnight. From there, you can calculate other julian day numbers. It supports negative values, and thus it will support more than 400 years. I believe you will start having to do corrections, at the time of the last Gregorian calendar reforms. If you go from Friday, 15 October 1582, and figure out its julian day number, and the reforms before and after that, you should be able to do all that you require. Be aware that the time of day runs "backwards" before 1899, but that this is purely a problem in human heads, the computer will be accurate, and will calculate the number of minutes and seconds, up to the limit of double precision floating point math for you. Stick with TDateTime as your base.
I found some really old BorlandPascal/TurboPascal code that handles a really wide range of dates here.
If you need to handle arabic, jewish, and other calendars, again, I refer you to Python as a great source of working examples. Not just the mxdatetime extension, but stuff like this.
For database persistence, you might want to base your date storage around julian day numbers, and your time as C-like seconds since midnight, if the maximum resolution you need is 1 second.
Here's a snippet I would start with, and do code completion on:
TCalendarDisplaySubtype = ( cdsGregorian,cdsHebrew,cdsArabic,cdsAztec,
cdsValveSoftwareCompany, cdsWhoTheHeckKnows );
TDateInformation = class
private
FBaseDateTime:TDateTime;
FYear,FMonth,FDay:Integer; // if -1 then not calculated yet.
FCalendarDisplaySubtype:TCalendarDisplaySubtype;
public
function SetByDateInCE(Y,M,D,h,m,s:Integer):Boolean;
function GetAsDateInCE(var Y,M,D,h,m,s:Integer):Boolean;
function DisplayStr:String;
function SetByDateInJewishCalendar( ... );
property BaseDateTime:TDateTime read FDateTime write FDateTime;
property JulianDayNumber:Integer read GetJulianDayNumber write SetJulianDayNumber;
property CalendarDisplaySubType:TCalendarDisplaySubtype;
end;
I see no reason to STORE both the julian day number, and the TDateTime, just use a constant, subtract/add from the Trunc(FBaseDateTime) value, and return that, in the GetJulianDayNumber,SetJulianDayNumber functions. It might be worth having fields where you calculate the year, month, day, for the given calendar, once, and store them, making the display as string function much simpler and faster.
Update: It looks like you're better at ER Modelling than me, so if you posted that diagram, I'd upvote it, and that would be it. As for me, I'd be storing three fields; A Datetime field that is normalized to modern calendar standards, a text field (free form) containing the original scholarly date in whatever form, and a few other fields, that are subtype lookup table Foreign keys, to help me organize, and search on dates by the date and subtype. That would be IT for me.
Only a partial answer but an important piece.
Since you are going to store dates in a very broad range where a lot of things happened to calendars, you need to accommodate for those changes.
The timezone database TZ-database and the Delphi TZDB wrapper around the TZ-database will be of big help.
It has a database with rules how timezones historically behave.
I know they are based on the current calendar schemes, and you need to convert to UTC first.
You need to devise something similar for the other calendar schemes you want to support.
Edit:
The scheme I'd use would be like this:
find ways for all your calendars to convert to/from UTC
store the calendar type
store the dates in their original format, and the source of the date (just in case your source screwed up, and you need to recalculate).
use the UTC conversions to go from your original through UTC to the calendar types in your UI
--jeroen
I have the date of birth of a person and want to calculate the days until his/her next birthday. How to do this in a way to deal with leapyears and other "odd" things?
Using google spreadsheet internal functions:
=IF(DATE(YEAR(TODAY()),MONTH(A2),DAY(A2))>TODAY(),
DATE(YEAR(TODAY()),MONTH(A2),DAY(A2)),
DATE(YEAR(TODAY())+1,MONTH(A2),DAY(A2)))
-TODAY()
where A2 is the cell with the birthday of the person.
The IF at the beginning is for testing if the next birthday is this year or next year.
A slightly shorter neater version using pure sheets functions is:
=DATE(YEAR(A2)+DATEDIF(A2,TODAY(),"y")+1,MONTH(A2),DAY(A2))-TODAY()
This simpler, and uses the DATEDIF(...,"y") to get complete years that have passed and adds one, rather than needing an If around the entire calculation.
Having figured this out working on the problem myself, I then came across the same solution on this site, which includes some more explanation.
following the nice and short version that Jon Egerton posted, here is a small change that returns 0 when the birthday is on the current day (instead of returning 365), and also handles future dates
=DATE(YEAR(A2)+IF(A2<TODAY(),DATEDIF(A2+1,TODAY(),"y")+1,-DATEDIF(TODAY(),A2,"y")),MONTH(A2),DAY(A2))-TODAY()
I found that using WolframAlpha for calculating the days is the most "simple" way to do it. Use the following code:
REGEXEXTRACT(JOIN("";ImportXML(JOIN("";"http://www.wolframalpha.com/input/?i=birthday+";YEAR(A2);"-";MONTH(A2);"-";DAY(A2);"&asynchronous=false&equal=Submit"); "//script")); "(\d+) days until next")
Where A2 is the cell with the birthday of the person.