Published
Edited
Aug 24, 2021
week = epiWeekOfDate(...date.split('-').map(d=>+d))
md`${date} is in epidemiological week #${week[1]} of ${week[0]}`
Inputs.table((weeks).map((d,i) => ({week: i+1, sunday: d.join("-"), saturday: adjustDate(d[0],d[1],d[2]+6).join("-")})));
weeks = epiWeeksOfYear(year)
function epiWeeksOfYear(y) {
let result = [];
let i = 1;
let firstDay = epiWeekFirstDay(y,i++);
while(firstDay[0] == y) {
result.push(firstDay);
firstDay = epiWeekFirstDay(y,i++);
}
return result;
}
function epiWeekFirstDay(y,weekIndex) {
let d0 = 1+(7-dow(y,1,1))%7;
return adjustDate(y,1,d0+7*(weekIndex-1));
}
function dow(y,m,d) {
// https://cs.uwaterloo.ca/~alopez-o/math-faq/node73.html
if(m<=2) {
m+=10;
y--;
} else {
m-=2;
}
const C = Math.floor(y/100);
y = y%100;
return (d+Math.floor((26*m-2)/10)-2*C+y+Math.floor(y/4)+Math.floor(C/4))%7;
}
function adjustDate(y,m,d) {
const ds = [31,((y%4==0)&&((y%100!=0)||(y%400==0))?29:28),31,30,31,30,31,31,30,31,30,31];
while(d > ds[m-1]) {
d = d-ds[m-1];
m++;
if(m>12) {
y++;
m=1;
}
}
return [y,m,d];
}
function epiWeekOfDate(y, m, d) {
const ds = [31,((y%4==0)&&((y%100!=0)||(y%400==0))?29:28),31,30,31,30,31,31,30,31,30,31];
for(let i=m-1; i>=1; i--) {
d+=ds[i-1];
}
let result = Math.floor((d - epiWeekFirstDay(y,1)[2])/7)+1;
if(result === 0) {
return epiWeekOfDate(y-1,12,31);
}
return [y,result];
}
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