source: Dev/trunk/src/client/dojox/math/stats.js

// AMD-ID "dojox/math/stats"
define(["dojo", "../main"], function(dojo, dojox) {
        
        dojo.getObject("math.stats", true, dojox);

        var st = dojox.math.stats;
        dojo.mixin(st, {
                sd: function(/* Number[] */a){
                        // summary:
                        //              Returns the standard deviation of the passed arguments.
                        return Math.sqrt(st.variance(a));       // Number
                },

                variance: function(/* Number[] */a){
                        // summary:
                        //              Find the variance in the passed array of numbers.
                        var mean=0, squares=0;
                        dojo.forEach(a, function(item){
                                mean+=item;
                                squares+=Math.pow(item,2);
                        });
                        return (squares/a.length)-Math.pow(mean/a.length, 2);   // Number
                },

                bestFit: function(/* Object[]|Number[] */ a, /* String? */ xProp, /* String? */ yProp){
                        // summary:
                        //              Calculate the slope and intercept in a linear fashion.  An array
                        //              of objects is expected; optionally you can pass in the property
                        //              names for "x" and "y", else x/y is used as the default.  If you
                        //              pass an array of numbers, it will be mapped to a set of {x,y} objects
                        //              where x = the array index.
                        xProp = xProp || "x", yProp = yProp || "y";
                        if(a[0] !== undefined && typeof(a[0]) == "number"){
                                // this is an array of numbers, so use the index as x.
                                a = dojo.map(a, function(item, idx){
                                        return { x: idx, y: item };
                                });
                        }

                        var sx = 0, sy = 0, sxx = 0, syy = 0, sxy = 0, stt = 0, sts = 0, n = a.length, t;
                        for(var i=0; i<n; i++){
                                sx += a[i][xProp];
                                sy += a[i][yProp];
                                sxx += Math.pow(a[i][xProp], 2);
                                syy += Math.pow(a[i][yProp], 2);
                                sxy += a[i][xProp] * a[i][yProp];
                        }

                        // we use the following because it's more efficient and accurate for determining the slope.
                        for(i=0; i<n; i++){
                                t = a[i][xProp] - sx/n;
                                stt += t*t;
                                sts += t*a[i][yProp];
                        }
                        var slope = sts/(stt||1);       // prevent divide by zero.

                        // get Pearson's R
                        var d = Math.sqrt((sxx - Math.pow(sx,2)/n) * (syy - Math.pow(sy,2)/n));
                        if(d === 0){
                                throw new Error("dojox.math.stats.bestFit: the denominator for Pearson's R is 0.");
                        }

                        var r = (sxy-(sx*sy/n)) / d;
                        var r2 = Math.pow(r, 2);
                        if(slope < 0){
                                r = -r;
                        }

                        // to use:  y = slope*x + intercept;
                        return {        // Object
                                slope: slope,
                                intercept: (sy - sx*slope)/(n||1),
                                r: r,
                                r2: r2
                        };
                },

                forecast: function(/* Object[]|Number[] */a, /* Number */x, /* String? */xProp, /* String? */yProp){
                        // summary:
                        //              Using the bestFit algorithm above, find y for the given x.
                        var fit = st.bestFit(a, xProp, yProp);
                        return (fit.slope * x) + fit.intercept; // Number
                },

                mean: function(/* Number[] */a){
                        // summary:
                        //              Returns the mean value in the passed array.
                        var t=0;
                        dojo.forEach(a, function(v){
                                t += v;
                        });
                        return t / Math.max(a.length, 1);       // Number
                },

                min: function(/* Number[] */a){
                        // summary:
                        //              Returns the min value in the passed array.
                        return Math.min.apply(null, a);         // Number
                },

                max: function(/* Number[] */a){
                        // summary:
                        //              Returns the max value in the passed array.
                        return Math.max.apply(null, a);         // Number
                },

                median: function(/* Number[] */a){
                        // summary:
                        //              Returns the value closest to the middle from a sorted version of the passed array.
                        var t = a.slice(0).sort(function(a, b){ return a - b; });
                        return (t[Math.floor(a.length/2)] + t[Math.ceil(a.length/2)])/2; // Number
                },

                mode: function(/* Number[] */a){
                        // summary:
                        //              Returns the mode from the passed array (number that appears the most often).
                        //              This is not the most efficient method, since it requires a double scan, but
                        //              is ensures accuracy.
                        var o = {}, r = 0, m = Number.MIN_VALUE;
                        dojo.forEach(a, function(v){
                                (o[v]!==undefined)?o[v]++:o[v]=1;
                        });

                        // we did the lookup map because we need the number that appears the most.
                        for(var p in o){
                                if(m < o[p]){
                                        m = o[p], r = p;
                                }
                        }
                        return r;       // Number
                },

                sum: function(/* Number[] */a){
                        // summary:
                        //              Return the sum of all the numbers in the passed array.  Does
                        //              not check to make sure values within a are NaN (should simply
                        //              return NaN).
                        var sum = 0;
                        dojo.forEach(a, function(n){
                                sum += n;
                        });
                        return sum;     // Number
                },

                approxLin: function(a, pos){
                        // summary:
                        //              Returns a linearly approximated value from an array using
                        //              a normalized float position value.
                        // a: Number[]
                        //              a sorted numeric array to be used for the approximation.
                        // pos: Number
                        //              a position number from 0 to 1. If outside of this range it
                        //              will be clamped.
                        // returns: Number
                        var p = pos * (a.length - 1), t = Math.ceil(p), f = t - 1;
                        if(f < 0){ return a[0]; }
                        if(t >= a.length){ return a[a.length - 1]; }
                        return a[f] * (t - p) + a[t] * (p - f); // Number
                },

                summary: function(a, alreadySorted){
                        // summary:
                        //              Returns a non-parametric collection of summary statistics:
                        //              the classic five-number summary extended to the Bowley's
                        //              seven-figure summary.
                        // a: Number[]
                        //              a numeric array to be appraised.
                        // alreadySorted: Boolean?
                        //              a Boolean flag to indicated that the array is already sorted.
                        //              This is an optional flag purely to improve the performance.
                        //              If skipped, the array will be assumed unsorted.
                        // returns: Object
                        if(!alreadySorted){
                                a = a.slice(0);                                                         // copy the array
                                a.sort(function(a, b){ return a - b; });        // sort it properly
                        }
                        var     l = st.approxLin,
                                result = {
                                        // the five-number summary
                                        min:    a[0],                           // minimum
                                        p25:    l(a, 0.25),                     // lower quartile
                                        med:    l(a, 0.5),                      // median
                                        p75:    l(a, 0.75),                     // upper quartile
                                        max:    a[a.length - 1],        // maximum
                                        // extended to the Bowley's seven-figure summary
                                        p10:    l(a, 0.1),                      // first decile
                                        p90:    l(a, 0.9)                       // last decile
                                };
                        return result;  // Object
                }
        });

        return dojox.math.stats;
});