Format A TimeSpan With Years

Question

I have a class with 2 date properties: FirstDay and LastDay. LastDay is nullable. I would like to generate a string in the format of "x year(s) y day(s)". If the total years are less than 1, I would like to omit the year section. If the total days are less than 1, I would like to omit the day section. If either years or days are 0, they should say "day/year", rather than "days/years" respectively.

Examples:
2.2 years:             "2 years 73 days"
1.002738 years:   "1 year 1 day"
0.2 years:             "73 days"
2 years:                "2 years"

What I have works, but it is long:

private const decimal DaysInAYear = 365.242M;  public string LengthInYearsAndDays {     get     {         var lastDay = this.LastDay ?? DateTime.Today;         var lengthValue = lastDay - this.FirstDay;          var builder = new StringBuilder();          var totalDays = (decimal)lengthValue.TotalDays;         var totalYears = totalDays / DaysInAYear;         var years = (int)Math.Floor(totalYears);          totalDays -= (years * DaysInAYear);         var days = (int)Math.Floor(totalDays);          Func<int, string> sIfPlural = value =>             value > 1 ? "s" : string.Empty;          if (years > 0)         {             builder.AppendFormat(                 CultureInfo.InvariantCulture,                 "{0} year{1}",                 years,                 sIfPlural(years));              if (days > 0)             {                 builder.Append(" ");             }         }          if (days > 0)         {             builder.AppendFormat(                 CultureInfo.InvariantCulture,                 "{0} day{1}",                 days,                 sIfPlural(days));         }          var length = builder.ToString();         return length;     } } 

Is there a more concise way of doing this (but still readable)?

Answer 1

A TimeSpan doesn't have a sensible concept of "years" because it depends on the start and end point. (Months is similar - how many months are there in 29 days? Well, it depends...)

To give a shameless plug, my Noda Time project makes this really simple though:

using System; using NodaTime;  public class Test {     static void Main(string[] args)     {         LocalDate start = new LocalDate(2010, 6, 19);         LocalDate end = new LocalDate(2013, 4, 11);         Period period = Period.Between(start, end,                                        PeriodUnits.Years | PeriodUnits.Days);          Console.WriteLine("Between {0} and {1} are {2} years and {3} days",                           start, end, period.Years, period.Days);     } } 

Output:

Between 19 June 2010 and 11 April 2013 are 2 years and 296 days 

Answer 2

public string GetAgeText(DateTime birthDate) {         const double ApproxDaysPerMonth = 30.4375;         const double ApproxDaysPerYear = 365.25;          /*         The above are the average days per month/year over a normal 4 year period         We use these approximations as they are more accurate for the next century or so         After that you may want to switch over to these 400 year approximations             ApproxDaysPerMonth = 30.436875            ApproxDaysPerYear  = 365.2425             How to get theese numbers:             The are 365 days in a year, unless it is a leepyear.             Leepyear is every forth year if Year % 4 = 0             unless year % 100 == 1             unless if year % 400 == 0 then it is a leep year.              This gives us 97 leep years in 400 years.              So 400 * 365 + 97 = 146097 days.             146097 / 400      = 365.2425             146097 / 400 / 12 = 30,436875          Due to the nature of the leap year calculation, on this side of the year 2100         you can assume every 4th year is a leap year and use the other approximatiotions          */     //Calculate the span in days     int iDays = (DateTime.Now - birthDate).Days;      //Calculate years as an integer division     int iYear = (int)(iDays / ApproxDaysPerYear);      //Decrease remaing days     iDays -= (int)(iYear * ApproxDaysPerYear);      //Calculate months as an integer division     int iMonths = (int)(iDays / ApproxDaysPerMonth);      //Decrease remaing days     iDays -= (int)(iMonths * ApproxDaysPerMonth);      //Return the result as an string        return string.Format("{0} years, {1} months, {2} days", iYear, iMonths, iDays); }