formatter->asDate() Year

#1

I was trying to format a date and was using

\Yii::$app->formatter->asDate($model->StartDt,‘M/d/Y’)

but as of the 28th of December, it started displaying the wrong year. Instead of 2020, it was displaying 2021.

I’ve fixed it by switching to

\Yii::$app->formatter->asDateTime($model->StartDt, ‘php:m/d/Y’)

but I’m trying to understand the why behind the issue and learn something.

after consulting the documentation

https://www.yiiframework.com/doc/api/2.0/yii-i18n-formatter#asDate()-detail
http://userguide.icu-project.org/formatparse/datetime

I see that Y -> year of “Week of Year” whereas y or yyyy -> year, but do not understand the difference. I haven’t been able to test using y and assume it would fix the issue, but would like to understand what ‘year of “Week of Year”’ is exactly. Can anyone enlighten me on this?

Thank you.

#2

Working with dates is a really complex thing, so for ISO 8601 they use a concept of date calculation based on weeks. Ubuntu Man Pages put it this way:

ISO 8601 week dates
%G, %g, and %V yield values calculated from the week-based year defined by the ISO 8601
standard. In this system, weeks start on a Monday, and are numbered from 01, for the
first week, up to 52 or 53, for the last week. Week 1 is the first week where four or
more days fall within the new year (or, synonymously, week 01 is: the first week of the
year that contains a Thursday; or, the week that has 4 January in it). When three of
fewer days of the first calendar week of the new year fall within that year, then the ISO
8601 week-based system counts those days as part of week 53 of the preceding year. For
example, 1 January 2010 is a Friday, meaning that just three days of that calendar week
fall in 2010. Thus, the ISO 8601 week-based system considers these days to be part of
week 53 (%V) of the year 2009 (%G); week 01 of ISO 8601 year 2010 starts on Monday, 4
January 2010.

A clear spot on the problem you pointed can be read on Wikipedia:

The first ISO week of a year may have up to three days that are actually in the Gregorian calendar year that is ending; if three, they are Monday, Tuesday and Wednesday.
– https://en.wikipedia.org/wiki/ISO_8601

So, 2020-12-28 was a Monday, belonging to the week year of 2021.

Another good read on the subject: What year it it? (A tale of ISO week dates)

2 Likes
#3

Oh, what a fantastic definition the week-based year has!! I never knew that.
Thank you @bpanatta.

1 Like
#4

Waw, interesting, I did not not that how to calculate 1st week.
So less than 4 days in a week breaking the year = previous year, more than 3 days = next year.

But it somehow does not fit for me here:

  • 28.12.2020 was monday … till 31.12.2020 thursday = 4 days = should belong to 2020 - right?