.OrderBy(DayOfWeek) to treat Sunday as the end of the week

Question

I'm ordering a number of objects by their System.DayOfWeek property.

DayOfWeek treats Sunday as the start of the week, whereas I would like it to be ordered so it appears at the end. It's just an enum, so I can't modify it. However I've read that I may be able to create a custom culture but think this is probably overkill.

List<TimeBand> orderedTimeBands = timeBands.OrderBy(x => x.DayName).ToList()

So DayName is a DayOfWeek, i want orderedTimeBands to be ordered from Monday -> Sunday.

Any ideas?

@TimSchmelter - Sorry if I wasn't clear, it's a `System.DayOfWeek` — m.edmondson, Sep 03 '13 at 11:28

score 54 · Accepted Answer · answered Sep 03 '13 at 11:25

54

The simplest approach would be:

var orderedTimeBands = timeBands.OrderBy(x => ((int) x.DayOfWeek + 6) % 7)
                                .ToList()

So we have:

Name        Original value      Value after arithmetic
Sunday       0                  6
Monday       1                  0
Tuesday      2                  1
Wednesday    3                  2
Thursday     4                  3
Friday       5                  4
Saturday     6                  5

... which is what you want, I think.

answered Sep 03 '13 at 11:25

Jon Skeet

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this ( +1 ) or as pointed out in http://stackoverflow.com/questions/3135587/c-set-initial-dayofweek-as-monday-not-sunday you could write a "custom" CurrentCulture and simply tell there that its monday – Najzero Sep 03 '13 at 11:27
@Najzero: Yes, the OP mentioned the custom culture idea in the question. I'd definitely consider that to be overkill. – Jon Skeet Sep 03 '13 at 11:27
Great example of thinking out of the box, glad you agree with me that a custom culture is overkill. Seems to work, I'll just make sure I put it in a method that describes why we're using addition and modulus to save future confusion. – m.edmondson Sep 03 '13 at 11:35

score 14 · Answer 2 · edited May 23 '17 at 12:02

I use a solution based on current culture:

// all days of week
var daysOfWeek = Enum.GetValues(typeof(DayOfWeek)).Cast<DayOfWeek>();

// get first day of week from current culture
var firstDayOfWeek = CultureInfo.CurrentCulture.DateTimeFormat.FirstDayOfWeek;

// all days of week ordered from first day of week
var daysOfWeekOrdered = daysOfWeek.OrderBy(x => (x - firstDayOfWeek + 7) % 7);

The important part is the OrderBy lambda. It's basically a parametrized version of Jon's answer above.

This way it will be ordered from Monday in the UK, and from Sunday in the US.

.OrderBy(DayOfWeek) to treat Sunday as the end of the week

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