Is there a simple equation I can replace this method with? - equation

Question

You input the day of the week as an int (sunday=0...saturday=6), and it outputs the number of days till the closest saturday.
If it's saturday, it returns 0 because it is saturday. If it's sunday, it returns -1 because it's 1 day past saturday. If it's friday, it returns 1 because it's 1 day into the future.
private int nightShiftTransform(int dayOfWeek)
{
switch (dayOfWeek)
{
case 0:
return -1;
case 1:
return -2;
case 2:
return -3;
case 3:
return 3;
case 4:
return 2;
case 5:
return 1;
case 6:
return 0;
default:
throw new Exception("Invalid day of week");
}
}
I hate this switch statement, but I can't figure out a simple equation I can replace it with.

Answer 1

I assume you're using C#.
A simple way :
private int nightShiftTransform(int dayOfWeek)
{
// ternary expression. You can do an if/else if you prefer
int result = (dayOfWeek >= 3 ? 6 - dayOfWeek : -(dayOfWeek + 1));
return result;
}

Answer 2

A simple way, if DayOfWeek is between 0 and 6;
result = 6 - DayOfWeek - 7*(DayOfWeek < 3);
assuming rules in C (i.e. an expression of the form DayOfWeek < 3 yields a value of 0 if false and 1 if true).

Answer 3

equation isn't a helpful tag. I'd make the language explicit. I can't tell if this is Java or C#.
If this were Java, I'd suggest using the Calendar constants rather than ints. I think it's more self documenting and readable.
I can't improve on carndacier's nice ternary expression:
package date;
import java.text.DateFormat;
import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.Arrays;
import java.util.Calendar;
import java.util.Date;
import java.util.List;
/**
* NightShiftDemo
* #author Michael
* #link https://stackoverflow.com/questions/33519165/is-there-a-simple-equation-i-can-replace-this-method-with
* #since 11/4/2015 5:21 AM
*/
public class NightShiftDemo {
public static void main(String[] args) {
try {
DateFormat formatter = new SimpleDateFormat("yyyy-MMM-dd");
List<String> dates = Arrays.asList("2015-Nov-01", "2015-Nov-02", "2015-Nov-03", "2015-Nov-04", "2015-Nov-05", "2015-Nov-06", "2015-Nov-07");
for (String date : dates) {
System.out.println(String.format("date: %s shift: %d", date, nightShiftTransform(formatter.parse(date))));
}
} catch (ParseException e) {
e.printStackTrace();
}
}
public static int nightShiftTransform(int dayOfWeek) throws Exception
{
switch (dayOfWeek)
{
case 0:
return -1;
case 1:
return -2;
case 2:
return -3;
case 3:
return 3;
case 4:
return 2;
case 5:
return 1;
case 6:
return 0;
default:
throw new Exception("Invalid day of week");
}
}
public static int nightShiftTransform(Date date) {
if (date == null) throw new IllegalArgumentException("date cannot be null");
Calendar calendar = Calendar.getInstance();
calendar.setTime(date);
int dayOfWeek = calendar.get(Calendar.DAY_OF_WEEK);
return ((dayOfWeek >= Calendar.WEDNESDAY) ? Calendar.SATURDAY - dayOfWeek : -dayOfWeek);
}
}