[removed] remove outlier from an array?

Question

values = [8160,8160,6160,22684,0,0,60720,1380,1380,57128]

how can I remove outliers like 0, 57218, 60720 and 22684?

Is there a library whic

Answer 1

This all depends on your interpretation of what an "outlier" is. A common approach:

• High outliers are anything beyond the 3rd quartile + 1.5 * the inter-quartile range (IQR)
• Low outliers are anything beneath the 1st quartile - 1.5 * IQR

This is also the approach described by Wolfram's Mathworld.

This is easily wrapped up in a function :) I've tried to write the below clearly; obvious refactoring opportunities do exist. Note that your given sample contains no outlying values using this common approach.

function filterOutliers(someArray) {  

    // Copy the values, rather than operating on references to existing values
    var values = someArray.concat();

    // Then sort
    values.sort( function(a, b) {
            return a - b;
         });

    /* Then find a generous IQR. This is generous because if (values.length / 4) 
     * is not an int, then really you should average the two elements on either 
     * side to find q1.
     */     
    var q1 = values[Math.floor((values.length / 4))];
    // Likewise for q3. 
    var q3 = values[Math.ceil((values.length * (3 / 4)))];
    var iqr = q3 - q1;

    // Then find min and max values
    var maxValue = q3 + iqr*1.5;
    var minValue = q1 - iqr*1.5;

    // Then filter anything beyond or beneath these values.
    var filteredValues = values.filter(function(x) {
        return (x <= maxValue) && (x >= minValue);
    });

    // Then return
    return filteredValues;
}