Get previous week number from php week number - php

Question

I currently need to get the previous week from a variable that passes a php week number so if it is week 13 I will get week 12.
The problem I am facing is that if I just minus 1 from the original number if I am in week 1 it will return week 0 unless I create an if statement ie:
if($week==1)
{
$prev_week=52;
$prev_year=$year-1;
}
This is assuming that php counts the weeks from 1 and not 0. This seems a bit clumsy and I was thinking there may be a better way of doing this utilizing PHP's many date and time functions.

Answer 1

Try this:
$currentWeek = date( 'W' );
$today = strtotime( date( 'Y-m-d' ) ) - 7*24*60*60; // last week this day
// change 7 to 30 to see last year's week numer
$lastWeek = date( 'W', $today );
echo $currentWeek . '--' . $lastWeek;
Hope this helps.
Update
$lastWeekNumber = date( 'W', strtotime( 'last week' ) );

Answer 2

$PreviousWeek = date("W",strtotime("-1 week"));

Answer 3

HamZa's and web-nomad's answers helped me to go a bit further and make sure, I get the right year. Using date ('Y') can lead to unexpected behavior since it can happen, that week 1 belongs to the next or the previous year according to ISO-8601 (which is what is used in Europe). Instead use date ('o'). Otherwise it can happen that you jump from week 52 to week 1 of the previous year (because the start of the week is in the previous year according to date ('Y').
$jahr = 2014; // jahr means year
$kw = 52; // kw contains week
Using date ('Y')returns:
previousWeek: 51-2014
currentWeek: 52-2014
nextWeek: 01-2014
Using date ('o')returns:
previousWeek: 51-2014
currentWeek: 52-2014
nextWeek: 01-2015
See all the code together, e. g. for building forward and backward-links:
$kwBack['kw'] = date ("W", strtotime ($jahr. 'W' . str_pad ($kw, 2, 0, STR_PAD_LEFT). ' -1 week'));
$kwBack['jahr'] = date ("o", strtotime ($jahr. 'W' . str_pad ($kw, 2, 0, STR_PAD_LEFT). ' -1 week'));
$kwNext['kw'] = date ("W", strtotime ($jahr. 'W' . str_pad ($kw, 2, 0, STR_PAD_LEFT). ' +1 week'));
$kwNext['jahr'] = date ("o", strtotime ($jahr. 'W' . str_pad ($kw, 2, 0, STR_PAD_LEFT). ' +1 week'));
echo "previousWeek: " . $kwBack['kw'] . "-" . $kwBack['jahr'];
echo "<br>currentWeek: " . $kw . "-" . $jahr;
echo "<br>nextWeek: " . $kwNext['kw'] . "-" . $kwNext['jahr'];
echo "<br>";
// Build the links
$urlBack = $_SERVER['PHP_SELF'] . "?" . http_build_query ($kwBack);
$urlNext = $_SERVER['PHP_SELF'] . "?" . http_build_query ($kwNext);
echo "Previous week: ". $urlBack . "<br>";
echo "Next week: ". $urlNext;

Answer 4

I think I could be over complicating the problem - basically I need to obtain results from the database that appear in the previous weeks from the selected week therefore if there is a possibility of 54 weeks in a year all I really need to do is:-
if($week==1)
{
$year_minsued=$year-1;
$week_minused=54;
}
else
{
$week_minused=$week-1;
$year_minused=$year;
}
My select statement can then read:
SELECT SUM(post_price), SUM(total_price) FROM
database_table
WHERE client_id='$account_no'
AND
(year<='$year_minused' AND week<='$week_minused')
I have not tested this as yet but thinks it should do the job.

Answer 5

We know that a year can be between 52 or 53 weeks. So, I created here a function that receives the current week and the current year. If this is true, it is obvious that the previous week will be the last week of the previous year, so through the variable year that I gave to this function, I subtract 1 to have the value or the previous year and I try to know how many weeks this year has, in this case that will be the week before week 1 for example. Otherwise, I subtract 1 in the value of the current week to have the value of the previous week.
i hope i have helped
function PreviusWeekNumber($ActualWeek, $Year){
if($ActualWeek === 1){
$TransformYearIntolastYear = $Year -1;
$date = new DateTime;
$date->setISODate($TransformYearIntolastYear, 53);
$Result = ($date->format("W") === "53" ? 53 : 52);
}else{
$Result = $ActualWeek -1;
}
return $Result;
}

Answer 6

Check this
$year = 2013; // Retrieved from the DB
$week = 1;
$prev_week = date("W",strtotime($year. 'W'.str_pad($week, 2, 0, STR_PAD_LEFT). ' -1 week'));
echo $prev_week; // returns 52
A demo which shows the year:
$year = 2013; // Retrieved from the DB
$week = 1;
$prev_week = date("W - Y",strtotime($year. 'W'.str_pad($week, 2, 0, STR_PAD_LEFT). ' -1 week'));
echo $prev_week; // returns 52 - 2012