Get last 'N' quarters in C#

Question

Suppose the current quater is 3 and the year is 2011. How can I get the last 5 quarters

Desired output:

Q3-2011
Q2-2011
Q1-2011
Q4-2010
Q3-2010

The Q and '-' is appended.

I am trying as under

int generateQuater = 5;

            int currentQuater = 3;//GetQuarter(DateTime.Now.Month);
            int currentYear = DateTime.Now.Year;

            List<string> lstQuaterYear = new List<string>();

            lstQuaterYear.Add(string.Concat('Q',currentQuater, '-', currentYear));

            for (int i = generateQuater; i > 0; i++)
            {
              //code to be placed   
            }

Thanks

Answer 1

public static IEnumerable Generate(int number, int currentYear, int currentQuarter)
{
    int counter = number;
    int quarter = currentQuarter;
    int year = currentYear;
    while (counter-- > 0)
    {
        yield return String.Format("Q{0}-{1}", year, quarter);
        quarter = quarter>1?quarter-1:4;
        year = quarter==4?year-1:year;
    }
}

Answer 2

Don't forget to refactor it :)

        int count = 5;

        int currentQuarter = GetQuarter(DateTime.Now.Month);
        int currentYear = DateTime.Now.Year;

        List<string> lstQuaterYear = new List<string>();

        for (int i = count; i > 0; i--)
        {
            lstQuaterYear.Add(string.Concat('Q', currentQuarter, '-', currentYear));
            currentQuarter--;
            if (currentQuarter == 0)
            {
                currentQuarter = 4;
                currentYear--;
            }
        }

Answer 3

You have to decrease your loop variable. The rest is not too difficult math. Its also not necessary to handle the first iteration in any special way:

for (int i = generateQuater; i > 0; i--)
{
    lstQuaterYear.Add(string.Format("Q{0}-{1}", currentQuater, currentYear));
    if (--currentQuater == 0)
    {
        currentQuater = 4;
        currentYear--;
    }
}

Answer 4

As a pure LINQ expression:

    public IEnumerable<String> GetQuarters(int start, int year, int count)
    {
        return (from q in Enumerable.Range(0, count)
                select String.Format("Q{0}-{1}", (start - q) + (((q + 1) / 4) * 4) , year - ((q + 1) / 4)));
    }

The math is somewhat ugly but does work, to use it you can just do:

foreach (String quarter in GetQuarters(3, 2011, 5))
{
   Console.WriteLine(quarter);
}

Answer 5

One way is to check for year roll over and then set the quarter to 4 and decrement the year:

int quarter=3;
int year=2011;
int count=5;
for(int i=0;i<count;i++)
{
   lstQuaterYear.Add(string.Format("Q{0} {1}", quarter, year);
   quarter--;
   if(quarter==0)
   {
     quarter=4;
     year--;
   }
}

Alternatively you could calculate a totalQuartal=year+quartal-1. Then decrement it on each step. And finally use year=totalQuartal/4 and quartal=totalQuartal%4+1. But I think the first way is easier to understand.

Answer 6

In case you should do some operations on the quarter period, like check if moment is within a quarter, you can use the Quarter class of the Time Period Library for .NET:

// ----------------------------------------------------------------------
public ITimePeriodCollection GetPastQuarters( int count )
{
  TimePeriodCollection quarters = new TimePeriodCollection();

  Quarter quarter = new Quarter();
  for ( int i = 0; i < count; i++ )
  {
    quarters.Add( quarter );
    quarter = quarter.GetPreviousQuarter();
  }

  return quarters;
} // GetPastQuarters