<?php
$date_list     = null;
$num_list     = null;
$index = 0;
while($index < 20) {
    $date_list[] = date('Y-m-d',strtotime('-' . $index . ' day'));
    $num_list[] = $index;
    $index++;
}

// 先别管上面的代码，只是为了生成你的数据
$ret_list = null;
// 假设日期数组和值数组的索引一致
foreach($date_list as $k => $date) {
    if($ret_list[date('W', strtotime($date))]) {
        $ret_list[date('W', strtotime($date))] += $num_list[$k];
    } else {
        $ret_list[date('W', strtotime($date))] = $num_list[$k];
    }
}
echo("日期数组：<br/>");
print_r($date_list);
echo("<br/>");

echo("数值数组：<br/>");
print_r($num_list);
echo("<br/>");

echo("按周统计数组（数组的键就是今年的第几周）：<br/>");
print_r($ret_list);

重点在于date函数的使用，如何获取日期属于年度的第几周，看看php的doc吧。

1）计算日期对应的周信息

function getWeekOfYear(date){
    var year=date.getFullYear();

    var baseDate=new Date(year,0,1);
    var baseWeekDay=testDate.getDay();

    var dateWeekDay=date.getDay();

    if(baseWeekDay==0) baseWeekDay=7;
    if(dateWeekDay==0) dateWeekDay=7;


    var weekOfYear=Math.round(((date.getTime()-dateWeekDay*3600*24*1000)-(baseDate.getTime()-baseWeekDay*3600*24*1000))/(24*3600*1000)/7);

    return weekOfYear+1;
}

2）将在同一周的数据相加

var dateArray=["2011-1-1","2011-1-2","2011-1-3","2014-10-01",'2014-01-01','2015-11-11'];
var dateTpArray=[9,8,7,6,121323445,23492742742374324];

var dateReg=/^(\d{4})\-(\d{1,2})\-(\d{1,2})$/;

var reduceResult={};
dateArray.forEach(function(item,index){
    var matchResult=dateReg.exec(item);
    console.log('%s %s %s',matchResult[1],matchResult[2],matchResult[3]);
    var weekOfYear=getWeekOfYear(new Date(parseInt(matchResult[1],10),parseInt(matchResult[2],10)-1,parseInt(matchResult[3],10)));
    if(!reduceResult[matchResult[1]+'_'+weekOfYear]){
        reduceResult[matchResult[1]+'_'+weekOfYear]={
            desc:matchResult[1]+'第'+weekOfYear+'周',
            tps:0
        }
    }
    reduceResult[matchResult[1]+'_'+weekOfYear].tps=reduceResult[matchResult[1]+'_'+weekOfYear].tps+dateTpArray[index];
});
var weekOfYearDescArray=[];
var weekofYearTpArray=[];
for(var prop in reduceResult){
    if(reduceResult.hasOwnProperty((prop))){
        weekOfYearDescArray.push(reduceResult[prop].desc);
        weekofYearTpArray.push(reduceResult[prop].tps);

    }
}

console.log(weekOfYearDescArray);
console.log(weekofYearTpArray);