Examples

var incrmean = require( '@stdlib/stats-incr-mean' );
var dataset = require( '@stdlib/datasets-cdc-nchs-us-births-1994-2003' );

function mean( a, b ) {
    return ( a + b ) / 2.0;
}

function reldiff( a, b ) {
    return 100.0 * ( (a-b)/a );
}

/*
* GOAL: determine whether people avoid giving birth on the 13th of each month.
*
* NOTE: for a more thorough analysis, we'd account for holidays.
*/

// Retrieve the data:
var data = dataset();

// Initialize arrays for storing births for particular day numbers:
var d6or20 = [ [], [], [], [], [], [], [] ];
var d13 = [ [], [], [], [], [], [], [] ];

// Extract the day number data...
var d;
var w;
var i;
for ( i = 0; i < data.length; i++ ) {
    d = data[ i ].date_of_month;
    w = data[ i ].day_of_week;
    if ( d === 6 ) {
        // Average of days 6 and 20 for the same month:
        d6or20[ w-1 ].push( mean( data[ i ].births, data[ i+14 ].births ) );
    } else if ( d === 13 ) {
        d13[ w-1 ].push( data[ i ].births );
    }
}

// Initialize accumulators for computing the average relative difference...
var means = [];
for ( i = 0; i < 7; i++ ) {
    means.push( incrmean() );
}

// Compute the average relative difference between days 6/20 with day 13...
var l1;
var l2;
var mu;
var j;
for ( i = 0; i < 7; i++ ) {
    l1 = d13[ i ];
    l2 = d6or20[ i ];
    mu = means[ i ];
    for ( j = 0; j < l1.length; j++ ) {
        mu( reldiff( l1[ j ], l2[ j ] ) );
    }
}

// Print the results...
for ( i = 0; i < 7; i++ ) {
    console.log( '%d: %d%', i+1, means[ i ]().toFixed( 3 ) );
}