Using Crossfilter, is it possible to track max/min when grouping?

Question

When using Crossfilter (https://github.com/square/crossfilter), I specify functions to use when adding and removing data from a group. It\'s fairly trivial to keep track of a ru

Answer 1

The best solution I came up with, was to keep track of all values in an ordered list and to add elements with a simple quicksort-style insertion function (cp. how to insert a number into a sorted array) and to remove them using indexOf.

Common functions:

function insertElement(element, array) {
    array.splice(locationOfElement(element, array) + 1, 0, element);
    return array;
}

function removeElement(element, array) {
    var index = array.indexOf(element);
    if (index >= 0) array.splice(index, 1);
    return array;
}

function locationOfElement(element, array, start, end) {
    start = start || 0;
    end = end || array.length;
    var pivot = parseInt(start + (end - start) / 2, 10);
    if (array[pivot] === element) return pivot;
    if (end - start <= 1)
        return array[pivot] > element ? pivot - 1 : pivot;
    if (array[pivot] < element) {
        return locationOfElement(element, array, pivot, end);
    } else {
        return locationOfElement(element, array, start, pivot);
    }
}

function maxElement(array) {
    return (array.length > 0) ? 
        array[array.length - 1] : null;
}

function minElement(array) {
    return (array.length > 0) ? 
        array[0] : null;
}

Functions to use when adding and removing data from a group to track min / max:

minMaxDimension = cf.dimension(function (d) {
    return d.key; 
});

var reduceAdd = function(p, v) {
    insertElement(v.value, p.elements);
    return p;
};

var reduceRemove = function(p, v) {
    removeElement(v.value, p.elements);
    return p;
};

var reduceInitial = function() {
    return { 
        elements: [],
        max: function() { return maxElement(elements); },
        min: function() { return minElement(elements); }
    }
}

minMaxGroup = minMaxDimension
    .group()
    .reduce(reduceAdd, reduceRemove, reduceInitial)
    .orderNatural()
    .top(Infinity);

Answer 2

You can use dimension.top(1) and dimension.bottom(1) to retrieve the current min and max. These methods respect any filters that may be active on the crossfilter.

Answer 3

After playing around with this for a bit, you can rebuild the group by just calling the group method again.