# LabVIEW

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## Week Number of the Year

Does anyone know of a function that will return the correct "Week" of the year when you enter a date?

I'm referencing this website:

https://www.timeanddate.com/date/weeknumber.html

I found Labview's "Format Date/Time String" calculates week one as 00.  It's not as simple as increment by one.

See attached VI

Anyway, is there any accurate way to repeat the correct Week Number of the Year?

Thank you,

Doug

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## Re: Week Number of the Year

%W: week number of the year (00–53), with the first Monday as the first day of week one; 00 represents the first week

%U: week number of the year (00–53), with the first Sunday as the first day of week one; 00 represents the first week.

So use %U and increment by one.

(Next time be more friendly and attach a VI that does not span about 3 screens wide. You could use arrays to simplify the code dramatically. Way too much duplication currently, making testing difficult ;))

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## Re: Week Number of the Year

@altenbach wrote:

%W: week number of the year (00–53), with the first Monday as the first day of week one; 00 represents the first week

%U: week number of the year (00–53), with the first Sunday as the first day of week one; 00 represents the first week.

So use %U and increment by one.

This works for this year, sure, but would fail on any year starting on a Sunday (2017, for instance).

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Thank you!

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## Re: Week Number of the Year

@Kyle97330 wrote:

@altenbach wrote:

%W: week number of the year (00–53), with the first Monday as the first day of week one; 00 represents the first week

%U: week number of the year (00–53), with the first Sunday as the first day of week one; 00 represents the first week.

So use %U and increment by one.

This works for this year, sure, but would fail on any year starting on a Sunday (2017, for instance).

You're right.  It seems like LabVIEW help doesn't describe this behavior.  But week 1 seems to be the first FULL week of the year.  So Sunday 1/1/17 starts a full week, it gets a 1 with %U format.  Monday 1/1/18 starts a full week with %W format.  Those years seem to have no 0 week.

Enumerating weeks of a year is a very unusual thing to do anyway.  It is more so to approximate how many weeks apart 2 different dates are by adding or subtracting.

And you can argue as to whether there should ever be a week 0 or not, and what that means if it exists.  If the week of year format isn't working the way you want for whatever purpose you have, then just wrap it in a subVI that modifies the results to your needs.

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## Re: Week Number of the Year

Here's what I had in mind.

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## Re: Week Number of the Year

I wasn't expecting answers so quickly, so I hacked my way around it.  I ended up adding one week and one day to get the correct week.  But, I'm sure it will be inaccurate at some point in time.

Wish there was an easier vi that simply took a date and gave the correct week year each and every time.

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## Re: Week Number of the Year

@Kyle97330 wrote:
This works for this year, sure, but would fail on any year starting on a Sunday (2017, for instance).

Fortunately, LabVIEW is a programming language and we can work around such edge issues if needed 😄

Message 8 of 27
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## Re: Week Number of the Year

The ISO 8601 standard for weeks states that “week 1” is the first week of the year with a Thursday in it.  Not sure if that's exactly what you want, but it would be nice if LabVIEW had that as an option.

If you are willing to use .NET there's an function that's more along the lines of what you need, with some configurable parameters to refine it:

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## Re: Week Number of the Year

Yes, I was reading up on the ISO definition. It's complicated. 😄

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