Question

I have two numbers; dates in Unix Epoch format.

Say I have two Unix Epoch timestamps:

1349422200 = 05/10/2012 08:30
1350489600 = 17/10/2012 17:00

I am able to find out how many days are between the two date/times, no problem.
What I would like to be able to work out is how many of those days are Saturdays or Sundays (Non-Weekdays). I’m sure there has to be an easy way to go about this but I can’t for the life of me figure it out without doing a load of for() loops.

Any help greatly appreciated.

Answer 1

Be more specific with your definition of weekend. Do you only want to include whole weekends (the entire 48 hour period of saturday and sunday)? Or does any range of time containing midnight on Friday night/Saturday morning count as a weekend? Do half weekends count as half, or do you round to the nearest whole number?

In any case:

1. Figure out what comprises a weekend
2. Find the first and last weekends in your range of time
3. Find the time difference between them, in days, and divide by 7

Edit: you’re seeking the exact amount of weekend time, with no rounding.

First, split the timespan into 3 chunks:

1. Everything from the beginning of the range up until the first possible Monday morning at midnight
2. Everything from the end of the previous block up to the last possible Monday morning at midnight
3. Everything from the end of the previous block to the end of the range

Then calculate the amount of weekend in each block, and sum them up.

1. The first block will contain no weekend time if it has a length of zero. If it has a length of 48 hours or less, its weekend time will equal its length. Otherwise, its weekend time will be 48 hours.
2. The middle block’s weekend time is its duration multiplied by 2/7 (trivial, since by our restrictions on its start and end, it is a whole number of weeks.)
3. The final block will contain no weekend time if its duration is less than or equal to five days. If its duration is greater than five days, its weekend time will equal its duration minus five days.

Special cases

If the block contains no monday midnights, consider the second and third blocks to have a length of zero. Find the beginning and the end of the one weekend inside the block (if it exists) and calculate the overlap.

If the block contains exactly one monday midnight, consider the first block the time before it, the second block to be of zero length, and the third block the time after it, and calculate as usual.