Question

I have data like the following:

var data = [{
   id: 1,
   date: new Date("2010-01-01"),
   value: 10
}, {
   id: 2,
   date: new Date("2010-01-01"),
   value: 11
}, {
   id: 3,
   date: new Date("2010-01-01"),
   value: 12
}, {
   id: 4,
   date: new Date("2010-01-02"),
   value: 10
}, {
   id: 5,
   date: new Date("2010-01-03"),
   value: 10
}, {
   id: 6,
   date: new Date("2010-01-03"),
   value: 21
}, {
   id: 7,
   date: new Date("2010-01-03"),
   value: 22
}, {
   id: 8,
   date: new Date("2010-01-03"),
   value: 23
}];

I am trying to apply two kinds of filters:

• Filter1 should give me only those points that differ by 1 in their value field but having the same date field. Therefore, this should return a new dataset containing data records with ids 1,2,3, 6,7,8 (the first three because values are 10,11,12 and last three because values are 21,22,23)
• Filter2 should give me only those points that differ by 1 day in their date field but having the same value field. Therefore, this should return a new dataset containing data records with ids 1,4,5

I am currently doing this in C# on the server-side but am looking to see if there is an efficient way to do this in Javascript. Any suggestions?

Answer 1

Why, custom sort functions, of course!

function filter1(arr) {
    // Clone the array:
    arr = arr.slice();

    // Sort the array by value:
    arr.sort(function(a, b) {
        return a.date - b.date || a.value - b.value;
    });

    // Look for consecutive elements with the same date:
    var r = [];

    for(var i = 1; i < arr.length; i++) {
        if(+arr[i - 1].date === +arr[i].date && arr[i - 1].value === arr[i].value - 1) {
            if(r.indexOf(arr[i - 1]) === -1) r.push(arr[i - 1]);
            r.push(arr[i]);
        }
    }

    // Return the result
    return r;
}

function filter2(arr) {
    // Clone the array:
    arr = arr.slice();

    // Sort the array by date:
    arr.sort(function(a, b) {
        return a.value - b.value || a.date - b.date;
    });

    // Look for consecutive elements with the same value:
    var r = [];

    for(var i = 1; i < arr.length; i++) {
        if(arr[i - 1].value === arr[i].value && arr[i].date - arr[i - 1].date <= 24 * 60 * 60 * 1000) {
            if(r.indexOf(arr[i - 1]) === -1) r.push(arr[i - 1]);
            r.push(arr[i]);
        }
    }

    // Return the result
    return r;
}