refactor: update stats/incr/wmean to handle nonnegative weights

lib/node_modules/@stdlib/stats/incr/wmean/lib/main.js

@@ -18,6 +18,14 @@
 
 'use strict';
 
+// MODULES //
+
+var isNonNegativeNumber = require( '@stdlib/assert/is-nonnegative-number' ).isPrimitive;
+var format = require( '@stdlib/string/format' );
+
+
+// MAIN //
+
 /**
 * Returns an accumulator function which incrementally computes a weighted arithmetic mean.
 *
@@ -97,7 +105,8 @@ function incrwmean() {
 	*
 	* @private
 	* @param {number} [x] - value
-	* @param {number} [w] - weight
+	* @param {NonNegativeNumber} [w] - weight
+	* @throws {TypeError} must provide a nonnegative number as the weight
 	* @returns {(number|null)} weighted mean or null
 	*/
 	function accumulator( x, w ) {
@@ -107,6 +116,12 @@ function incrwmean() {
 			}
 			return mu;
 		}
+		if ( !isNonNegativeNumber( w ) ) {
+			throw new TypeError( format( 'invalid argument. Must provide a nonnegative weight. Weight: `%s`.', w ) );
+		}
+		if (w === 0.0) {
+			return ( FLG === void 0 ) ? null : mu;
+		}
 		FLG = true;
 		wsum += w;
 		mu += ( w/wsum ) * ( x-mu );

lib/node_modules/@stdlib/stats/incr/wmean/test/test.js

@@ -46,6 +46,47 @@ tape( 'the initial accumulated value is `null`', function test( t ) {
 	t.end();
 });
 
+tape( 'the accumulator function ignores zero weights and only updates the mean after encountering a non-zero weight', function test( t ) {
+	var acc = incrwmean();
+	t.equal( acc(), null, 'returns expected value' );
+	t.equal( acc( 2.0, 0.0 ), null, 'returns the previous accumulated mean' );
+	t.equal( acc( 2.0, 2.0 ), 2.0, 'returns the current accumulated mean' );
+	t.equal( acc( 5.0, 0.0 ), 2.0, 'returns the previous accumulated mean' );
+	t.end();
+});
+
+tape( 'the function throws an error if not provided a nonnegative number', function test( t ) {
+	var values;
+	var acc;
+	var i;
+
+	values = [
+		'5',
+		-5.0,
+		NaN,
+		undefined,
+		true,
+		false,
+		null,
+		void 0,
+		[],
+		{},
+		function noop() {}
+	];
+
+	for ( i = 0; i < values.length; i++ ) {
+		t.throws( badValue( values[i] ), TypeError, 'throws an error when provided '+values[i] );
+	}
+	t.end();
+
+	function badValue( value ) {
+		return function badValue() {
+			acc = incrwmean();
+			acc( 2.0, value );
+		};
+	}
+});
+
 tape( 'the accumulator function incrementally computes a weighted arithmetic mean', function test( t ) {
 	var expected;
 	var actual;
@@ -99,24 +140,9 @@ tape( 'if not provided arguments, the accumulator function returns the current w
 	t.end();
 });
 
-tape( 'if not provided a weight, the accumulator function returns `NaN`', function test( t ) {
+tape( 'if provided `NaN` for a value, the accumulator function returns `NaN`', function test( t ) {
 	var acc = incrwmean();
-	t.equal( isnan( acc( 2.0 ) ), true, 'returns NaN' );
-	t.equal( isnan( acc( 3.14 ) ), true, 'returns NaN' );
-	t.end();
-});
-
-tape( 'if provided `NaN` for either a value or a weight, the accumulator function returns `NaN`', function test( t ) {
-	var acc = incrwmean();
-	t.equal( isnan( acc( 2.0, NaN ) ), true, 'returns NaN' );
-	t.equal( isnan( acc( 3.14, NaN ) ), true, 'returns NaN' );
-
-	acc = incrwmean();
 	t.equal( isnan( acc( NaN, 1.0 ) ), true, 'returns NaN' );
 	t.equal( isnan( acc( NaN, 1.0 ) ), true, 'returns NaN' );
-
-	acc = incrwmean();
-	t.equal( isnan( acc( NaN, NaN ) ), true, 'returns NaN' );
-	t.equal( isnan( acc( NaN, NaN ) ), true, 'returns NaN' );
 	t.end();
 });