diff --git a/lib/node_modules/@stdlib/stats/incr/nanskewness/README.md b/lib/node_modules/@stdlib/stats/incr/nanskewness/README.md
new file mode 100644
index 000000000000..300bb91f0fc6
--- /dev/null
+++ b/lib/node_modules/@stdlib/stats/incr/nanskewness/README.md
@@ -0,0 +1,232 @@
+
+
+# incrnanskewness
+
+> Compute a [corrected sample skewness][sample-skewness] incrementally.
+
+
+
+The [skewness][sample-skewness] for a random variable `X` is defined as
+
+
+
+```math
+\mathop{\mathrm{Skewness}}[X] = \mathrm{E}\biggl[ \biggl( \frac{X - \mu}{\sigma} \biggr)^3 \biggr]
+```
+
+
+
+
+
+For a sample of `n` values, the [sample skewness][sample-skewness] is
+
+
+
+```math
+b_1 = \frac{m_3}{s^3} = \frac{\frac{1}{n} \sum_{i=0}^{n-1} (x_i - \bar{x})^3}{\biggl( \frac{1}{n-1} \sum_{i=0}^{n-1} (x_i - \bar{x})^2 \biggr)^{3/2}}
+```
+
+
+
+
+
+where `m_3` is the sample third central moment and `s` is the sample standard deviation.
+
+An alternative definition for the [sample skewness][sample-skewness] which includes an adjustment factor (and is the implemented definition) is
+
+
+
+```math
+G_1 = \frac{n^2}{(n-1)(n-2)} \frac{m_3}{s^3} = \frac{\sqrt{n(n-1)}}{n-2} \frac{\frac{1}{n} \sum_{i=0}^{n-1} (x_i - \bar{x})^3}{\biggl( \frac{1}{n} \sum_{i=0}^{n-1} (x_i - \bar{x})^2 \biggr)^{3/2}}
+```
+
+
+
+
+
+
+
+
+
+
+
+## Usage
+
+```javascript
+var incrnanskewness = require( '@stdlib/stats/incr/skewness' );
+```
+
+#### incrnanskewness()
+
+Returns an accumulator `function` which incrementally computes a [corrected sample skewness][sample-skewness].
+
+```javascript
+var accumulator = incrnanskewness();
+```
+
+#### accumulator( \[x] )
+
+If provided an input value `x`, the accumulator function returns an updated [corrected sample skewness][sample-skewness]. If not provided an input value `x`, the accumulator function returns the current [corrected sample skewness][sample-skewness].
+
+
+
+```javascript
+var accumulator = incrnanskewness();
+
+var skewness = accumulator();
+// returns null
+
+skewness = accumulator(2.0);
+// returns null
+
+skewness = accumulator(-5.0);
+// returns null
+
+skewness = accumulator(-10.0);
+// returns ~0.492
+
+skewness = accumulator( NaN );
+// returns ~0.492
+
+skewness = accumulator();
+// returns ~0.492
+```
+
+
+
+
+
+
+
+
+
+## Notes
+
+- Input values are **not** type checked. If non-numeric inputs are possible, you are advised to type check and handle accordingly **before** passing the value to the accumulator function.
+
+- For long running accumulations or accumulations of large numbers, care should be taken to prevent overflow.
+
+
+
+
+
+
+
+## Examples
+
+
+
+
+
+```javascript
+var randu = require( '@stdlib/random/base/randu' );
+var incrnanskewness = require( '@stdlib/stats/incr/lib' );
+
+var accumulator;
+var skewness;
+var v;
+var i;
+
+// Initialize an accumulator:
+accumulator = incrnanskewness();
+
+// For each simulated datum, update the skewness...
+console.log('\nValue\tSkewness\n');
+for (i = 0; i < 100; i++) {
+ if (randu() < 0.2) {
+ v = NaN;
+ } else {
+ v = randu() * 100.0;
+ }
+ skewness = accumulator(v);
+ console.log( '%d\t%s', v.toFixed(4), (skewness === null) ? 'NaN' : skewness.toFixed(4));
+}
+console.log('\nFinal skewness: %s\n', accumulator());
+```
+
+
+
+
+
+
+
+* * *
+
+
+
+## References
+
+- Joanes, D. N., and C. A. Gill. 1998. "Comparing measures of sample skewness and kurtosis."
+- Journal of the Royal Statistical Society: Series D (The Statistician)_ 47 (1). Blackwell Publishers Ltd: 183–89. doi:[10.1111/1467-9884.00122][@joanes:1998].
+
+
+
+
+
+
+
+
+
+* * *
+
+## See Also
+
+- [`@stdlib/stats/incr/skewness`][@stdlib/stats/incr/skewness]: compute a corrected sample skewness incrementally.
+- [`@stdlib/stats/incr/kurtosis`][@stdlib/stats/incr/kurtosis]: compute a corrected sample excess kurtosis incrementally.
+- [`@stdlib/stats/incr/mean`][@stdlib/stats/incr/mean]: compute an arithmetic mean incrementally.
+- [`@stdlib/stats/incr/stdev`][@stdlib/stats/incr/stdev]: compute a corrected sample standard deviation incrementally.
+- [`@stdlib/stats/incr/summary`][@stdlib/stats/incr/summary]: compute a statistical summary incrementally.
+- [`@stdlib/stats/incr/variance`][@stdlib/stats/incr/variance]: compute an unbiased sample variance incrementally.
+
+
+
+
+
+
+
+
+
+[sample-skewness]: https://en.wikipedia.org/wiki/Skewness
+[@joanes:1998]: http://onlinelibrary.wiley.com/doi/10.1111/1467-9884.00122/
+
+
+
+[@stdlib/stats/incr/skewness]: https://github.com/stdlib-js/stdlib/tree/develop/lib/node_modules/%40stdlib/stats/incr/skewness
+[@stdlib/stats/incr/kurtosis]: https://github.com/stdlib-js/stdlib/tree/develop/lib/node_modules/%40stdlib/stats/incr/kurtosis
+[@stdlib/stats/incr/mean]: https://github.com/stdlib-js/stdlib/tree/develop/lib/node_modules/%40stdlib/stats/incr/mean
+[@stdlib/stats/incr/stdev]: https://github.com/stdlib-js/stdlib/tree/develop/lib/node_modules/%40stdlib/stats/incr/stdev
+[@stdlib/stats/incr/summary]: https://github.com/stdlib-js/stdlib/tree/develop/lib/node_modules/%40stdlib/stats/incr/summary
+[@stdlib/stats/incr/variance]: https://github.com/stdlib-js/stdlib/tree/develop/lib/node_modules/%40stdlib/stats/incr/variance
+
+
+
+
+
+
diff --git a/lib/node_modules/@stdlib/stats/incr/nanskewness/benchmark/benchmark.js b/lib/node_modules/@stdlib/stats/incr/nanskewness/benchmark/benchmark.js
new file mode 100644
index 000000000000..8117c341a953
--- /dev/null
+++ b/lib/node_modules/@stdlib/stats/incr/nanskewness/benchmark/benchmark.js
@@ -0,0 +1,69 @@
+/**
+* @license Apache-2.0
+*
+* Copyright (c) 2020 The Stdlib Authors.
+*
+* Licensed under the Apache License, Version 2.0 (the "License");
+* you may not use this file except in compliance with the License.
+* You may obtain a copy of the License at
+*
+* http://www.apache.org/licenses/LICENSE-2.0
+*
+* Unless required by applicable law or agreed to in writing, software
+* distributed under the License is distributed on an "AS IS" BASIS,
+* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+* See the License for the specific language governing permissions and
+* limitations under the License.
+*/
+
+'use strict';
+
+// MODULES //
+
+var bench = require( '@stdlib/bench' );
+var randu = require( '@stdlib/random/base/randu' );
+var pkg = require( './../package.json' ).name;
+var incrnanskewness = require( './../lib' );
+
+
+// MAIN //
+
+bench( pkg, function benchmark( b ) {
+ var f;
+ var i;
+ b.tic();
+ for ( i = 0; i < b.iterations; i++ ) {
+ f = incrnanskewness();
+ if ( typeof f !== 'function' ) {
+ b.fail( 'should return a function' );
+ }
+ }
+ b.toc();
+ if ( typeof f !== 'function' ) {
+ b.fail( 'should return a function' );
+ }
+ b.pass( 'benchmark finished' );
+ b.end();
+});
+
+bench( pkg+'::accumulator', function benchmark( b ) {
+ var acc;
+ var v;
+ var i;
+
+ acc = incrnanskewness();
+
+ b.tic();
+ for ( i = 0; i < b.iterations; i++ ) {
+ v = acc( randu() );
+ if ( v !== v ) {
+ b.fail( 'should not return NaN' );
+ }
+ }
+ b.toc();
+ if ( v !== v ) {
+ b.fail( 'should not return NaN' );
+ }
+ b.pass( 'benchmark finished' );
+ b.end();
+});
diff --git a/lib/node_modules/@stdlib/stats/incr/nanskewness/docs/img/equation_adjusted_sample_skewness.svg b/lib/node_modules/@stdlib/stats/incr/nanskewness/docs/img/equation_adjusted_sample_skewness.svg
new file mode 100644
index 000000000000..3277353af222
--- /dev/null
+++ b/lib/node_modules/@stdlib/stats/incr/nanskewness/docs/img/equation_adjusted_sample_skewness.svg
@@ -0,0 +1,171 @@
+
\ No newline at end of file
diff --git a/lib/node_modules/@stdlib/stats/incr/nanskewness/docs/img/equation_sample_skewness.svg b/lib/node_modules/@stdlib/stats/incr/nanskewness/docs/img/equation_sample_skewness.svg
new file mode 100644
index 000000000000..147334d80f8b
--- /dev/null
+++ b/lib/node_modules/@stdlib/stats/incr/nanskewness/docs/img/equation_sample_skewness.svg
@@ -0,0 +1,131 @@
+
\ No newline at end of file
diff --git a/lib/node_modules/@stdlib/stats/incr/nanskewness/docs/img/equation_skewness.svg b/lib/node_modules/@stdlib/stats/incr/nanskewness/docs/img/equation_skewness.svg
new file mode 100644
index 000000000000..45650ae35b70
--- /dev/null
+++ b/lib/node_modules/@stdlib/stats/incr/nanskewness/docs/img/equation_skewness.svg
@@ -0,0 +1,59 @@
+
\ No newline at end of file
diff --git a/lib/node_modules/@stdlib/stats/incr/nanskewness/docs/repl.txt b/lib/node_modules/@stdlib/stats/incr/nanskewness/docs/repl.txt
new file mode 100644
index 000000000000..d6d6b7542e3c
--- /dev/null
+++ b/lib/node_modules/@stdlib/stats/incr/nanskewness/docs/repl.txt
@@ -0,0 +1,31 @@
+
+{{alias}}()
+ Returns an accumulator function which incrementally computes a corrected
+ sample skewness, ignoring NaN values.
+
+ If provided a value, the accumulator function returns an updated corrected
+ sample skewness. If not provided a value, the accumulator function returns
+ the current corrected sample skewness.
+
+ Returns
+ -------
+ acc: Function
+ Accumulator function.
+
+ Examples
+ --------
+ > var accumulator = {{alias}}();
+ > var v = accumulator( 2.0 )
+ null
+ > v = accumulator( -5.0 )
+ null
+ > v = accumulator( -10.0 )
+ ~0.492
+ > v = accumulator( NaN )
+ ~0.492
+ > v = accumulator()
+ ~0.492
+
+ See Also
+ --------
+
diff --git a/lib/node_modules/@stdlib/stats/incr/nanskewness/docs/types/index.d.ts b/lib/node_modules/@stdlib/stats/incr/nanskewness/docs/types/index.d.ts
new file mode 100644
index 000000000000..384d6311795e
--- /dev/null
+++ b/lib/node_modules/@stdlib/stats/incr/nanskewness/docs/types/index.d.ts
@@ -0,0 +1,68 @@
+/*
+* @license Apache-2.0
+*
+* Copyright (c) 2019 The Stdlib Authors.
+*
+* Licensed under the Apache License, Version 2.0 (the "License");
+* you may not use this file except in compliance with the License.
+* You may obtain a copy of the License at
+*
+* http://www.apache.org/licenses/LICENSE-2.0
+*
+* Unless required by applicable law or agreed to in writing, software
+* distributed under the License is distributed on an "AS IS" BASIS,
+* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+* See the License for the specific language governing permissions and
+* limitations under the License.
+*/
+
+// TypeScript Version: 4.1
+
+///
+
+/**
+* If provided a value, the accumulator function returns an updated corrected sample skewness. If not provided a value, the accumulator function returns the current corrected sample skewness.
+*
+* ## Notes
+*
+* - If provided `NaN` or a value which, when used in computations, results in `NaN`, the accumulated value is `NaN` for all future invocations.
+*
+* @param x - value
+* @returns corrected sample skewness or null
+*/
+type accumulator = ( x?: number ) => number | null;
+
+/**
+* Returns an accumulator function which incrementally computes a corrected sample skewness.
+*
+* ## Notes
+*
+* - If provided a value, the accumulator function returns an updated corrected sample skewness. If not provided a value, the accumulator function returns the current corrected sample skewness.
+* - If provided `NaN` or a value which, when used in computations, results in `NaN`, the accumulated value is `NaN` for all future invocations.
+*
+* @returns accumulator function
+*
+* @example
+* var accumulator = incrskewness();
+*
+* var skewness = accumulator();
+* // returns null
+*
+* skewness = accumulator( 2.0 );
+* // returns null
+*
+* skewness = accumulator( -5.0 );
+* // returns null
+*
+* skewness = accumulator( -10.0 );
+* // returns ~0.492
+*
+* skewness = accumulator();
+* // returns ~0.492
+*/
+declare function incrskewness(): accumulator;
+
+
+// EXPORTS //
+
+export = incrskewness;
diff --git a/lib/node_modules/@stdlib/stats/incr/nanskewness/docs/types/test.ts b/lib/node_modules/@stdlib/stats/incr/nanskewness/docs/types/test.ts
new file mode 100644
index 000000000000..a2ef30a7fa56
--- /dev/null
+++ b/lib/node_modules/@stdlib/stats/incr/nanskewness/docs/types/test.ts
@@ -0,0 +1,61 @@
+/*
+* @license Apache-2.0
+*
+* Copyright (c) 2019 The Stdlib Authors.
+*
+* Licensed under the Apache License, Version 2.0 (the "License");
+* you may not use this file except in compliance with the License.
+* You may obtain a copy of the License at
+*
+* http://www.apache.org/licenses/LICENSE-2.0
+*
+* Unless required by applicable law or agreed to in writing, software
+* distributed under the License is distributed on an "AS IS" BASIS,
+* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+* See the License for the specific language governing permissions and
+* limitations under the License.
+*/
+
+import incrnanskewness = require( './index' );
+
+
+// TESTS //
+
+// The function returns an accumulator function...
+{
+ incrnanskewness(); // $ExpectType accumulator
+}
+
+// The compiler throws an error if the function is provided invalid arguments...
+{
+ incrnanskewness( '5' ); // $ExpectError
+ incrnanskewness( true ); // $ExpectError
+ incrnanskewness( false ); // $ExpectError
+ incrnanskewness( null ); // $ExpectError
+ incrnanskewness( [] ); // $ExpectError
+ incrnanskewness( {} ); // $ExpectError
+ incrnanskewness( ( x: number ): number => x ); // $ExpectError
+}
+
+// The function returns an accumulator function which returns an accumulated result...
+{
+ const acc = incrnanskewness();
+
+ acc(); // $ExpectType number | null
+ acc( 2 ); // $ExpectType number | null
+ acc( -5 ); // $ExpectType number | null
+ acc( 10 ); // $ExpectType number | null
+}
+
+// The compiler throws an error if the returned accumulator function is provided invalid arguments...
+{
+ const acc = incrnanskewness();
+
+ acc( '5' ); // $ExpectError
+ acc( true ); // $ExpectError
+ acc( false ); // $ExpectError
+ acc( null ); // $ExpectError
+ acc( [] ); // $ExpectError
+ acc( {} ); // $ExpectError
+ acc( ( x: number ): number => x ); // $ExpectError
+}
diff --git a/lib/node_modules/@stdlib/stats/incr/nanskewness/examples/index.js b/lib/node_modules/@stdlib/stats/incr/nanskewness/examples/index.js
new file mode 100644
index 000000000000..88b03efd4ff1
--- /dev/null
+++ b/lib/node_modules/@stdlib/stats/incr/nanskewness/examples/index.js
@@ -0,0 +1,43 @@
+/**
+* @license Apache-2.0
+*
+* Copyright (c) 2020 The Stdlib Authors.
+*
+* Licensed under the Apache License, Version 2.0 (the "License");
+* you may not use this file except in compliance with the License.
+* You may obtain a copy of the License at
+*
+* http://www.apache.org/licenses/LICENSE-2.0
+*
+* Unless required by applicable law or agreed to in writing, software
+* distributed under the License is distributed on an "AS IS" BASIS,
+* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+* See the License for the specific language governing permissions and
+* limitations under the License.
+*/
+
+'use strict';
+
+var randu = require( '@stdlib/random/base/randu' );
+var incrnanskewness = require( './../lib' );
+
+var accumulator;
+var skewness;
+var v;
+var i;
+
+// Initialize an accumulator:
+accumulator = incrnanskewness();
+
+// For each simulated datum, update the skewness...
+console.log( '\nValue\tSkewness\n' );
+for ( i = 0; i < 100; i++ ) {
+ if ( randu() < 0.2 ) {
+ v = NaN;
+ } else {
+ v = randu() * 100.0;
+ }
+ skewness = accumulator( v );
+ console.log( '%d\t%s', v.toFixed( 4 ), ( skewness === null ) ? 'NaN' : skewness.toFixed( 4 ) );
+}
+console.log( '\nFinal skewness: %s\n', accumulator() );
diff --git a/lib/node_modules/@stdlib/stats/incr/nanskewness/lib/index.js b/lib/node_modules/@stdlib/stats/incr/nanskewness/lib/index.js
new file mode 100644
index 000000000000..978dd6185a95
--- /dev/null
+++ b/lib/node_modules/@stdlib/stats/incr/nanskewness/lib/index.js
@@ -0,0 +1,57 @@
+/**
+* @license Apache-2.0
+*
+* Copyright (c) 2020 The Stdlib Authors.
+*
+* Licensed under the Apache License, Version 2.0 (the "License");
+* you may not use this file except in compliance with the License.
+* You may obtain a copy of the License at
+*
+* http://www.apache.org/licenses/LICENSE-2.0
+*
+* Unless required by applicable law or agreed to in writing, software
+* distributed under the License is distributed on an "AS IS" BASIS,
+* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+* See the License for the specific language governing permissions and
+* limitations under the License.
+*/
+
+'use strict';
+
+/**
+* Compute a skewness incrementally, ignoring `NaN` values.
+*
+* @module @stdlib/stats/incr/nanskewness
+*
+* @example
+* var incrnanskewness = require( '@stdlib/stats/incr/nanskewness' );
+*
+* var accumulator = incrnanskewness();
+*
+* var skewness = accumulator();
+* // returns null
+*
+* skewness = accumulator( 2.0 );
+* // returns null
+*
+* skewness = accumulator( -5.0 );
+* // returns null
+*
+* skewness = accumulator( -10.0 );
+* // returns ~0.492
+*
+* skewness = accumulator( NaN );
+* // returns ~0.492
+*
+* skewness = accumulator();
+* // returns ~0.492
+*/
+
+// MODULES //
+
+var main = require( './main.js' );
+
+
+// EXPORTS //
+
+module.exports = main;
diff --git a/lib/node_modules/@stdlib/stats/incr/nanskewness/lib/main.js b/lib/node_modules/@stdlib/stats/incr/nanskewness/lib/main.js
new file mode 100644
index 000000000000..0d5ddf1af93f
--- /dev/null
+++ b/lib/node_modules/@stdlib/stats/incr/nanskewness/lib/main.js
@@ -0,0 +1,74 @@
+/**
+* @license Apache-2.0
+*
+* Copyright (c) 2020 The Stdlib Authors.
+*
+* Licensed under the Apache License, Version 2.0 (the "License");
+* you may not use this file except in compliance with the License.
+* You may obtain a copy of the License at
+*
+* http://www.apache.org/licenses/LICENSE-2.0
+*
+* Unless required by applicable law or agreed to in writing, software
+* distributed under the License is distributed on an "AS IS" BASIS,
+* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+* See the License for the specific language governing permissions and
+* limitations under the License.
+*/
+
+'use strict';
+
+// MODULES //
+
+var isnan = require( '@stdlib/math/base/assert/is-nan' );
+var incrskewness = require( '@stdlib/stats/incr/skewness' );
+
+
+// MAIN //
+
+/**
+* Returns an accumulator function which incrementally computes skewness, ignoring `NaN` values.
+*
+* @returns {Function} accumulator function
+*
+* @example
+* var accumulator = incrskewness();
+
+* var skewness = accumulator();
+* // returns null
+
+* skewness = accumulator( 2.0 );
+* // returns null
+
+* skewness = accumulator( -5.0 );
+* // returns null
+
+* skewness = accumulator( -10.0 );
+* // returns ~0.492
+
+* skewness = accumulator();
+* // returns ~0.492
+*/
+function incrnanskewness() {
+ var skewness = incrskewness();
+ return accumulator;
+
+ /**
+ * If provided a value, the accumulator function returns an updated skewness. If not provided a value, the accumulator function returns the current skewness.
+ *
+ * @private
+ * @param {number} [x] - new value
+ * @returns {(number|null)} skewness or null
+ */
+ function accumulator( x ) {
+ if ( arguments.length === 0 || isnan( x ) ) {
+ return skewness();
+ }
+ return skewness( x );
+ }
+}
+
+
+// EXPORTS //
+
+module.exports = incrnanskewness;
diff --git a/lib/node_modules/@stdlib/stats/incr/nanskewness/package.json b/lib/node_modules/@stdlib/stats/incr/nanskewness/package.json
new file mode 100644
index 000000000000..7f14e4f6a707
--- /dev/null
+++ b/lib/node_modules/@stdlib/stats/incr/nanskewness/package.json
@@ -0,0 +1,65 @@
+{
+ "name": "@stdlib/stats/incr/nanskewness",
+ "version": "0.0.0",
+ "description": "Compute a corrected sample skewness incrementally.",
+ "license": "Apache-2.0",
+ "author": {
+ "name": "The Stdlib Authors",
+ "url": "https://github.com/stdlib-js/stdlib/graphs/contributors"
+ },
+ "contributors": [
+ {
+ "name": "The Stdlib Authors",
+ "url": "https://github.com/stdlib-js/stdlib/graphs/contributors"
+ }
+ ],
+ "main": "./lib",
+ "directories": {
+ "benchmark": "./benchmark",
+ "doc": "./docs",
+ "example": "./examples",
+ "lib": "./lib",
+ "test": "./test"
+ },
+ "types": "./docs/types",
+ "scripts": {},
+ "homepage": "https://github.com/stdlib-js/stdlib",
+ "repository": {
+ "type": "git",
+ "url": "git://github.com/stdlib-js/stdlib.git"
+ },
+ "bugs": {
+ "url": "https://github.com/stdlib-js/stdlib/issues"
+ },
+ "dependencies": {},
+ "devDependencies": {},
+ "engines": {
+ "node": ">=0.10.0",
+ "npm": ">2.7.0"
+ },
+ "os": [
+ "aix",
+ "darwin",
+ "freebsd",
+ "linux",
+ "macos",
+ "openbsd",
+ "sunos",
+ "win32",
+ "windows"
+ ],
+ "keywords": [
+ "stdlib",
+ "stdmath",
+ "statistics",
+ "stats",
+ "mathematics",
+ "math",
+ "skewness",
+ "sample skewness",
+ "shape",
+ "corrected",
+ "incremental",
+ "accumulator"
+ ]
+}
diff --git a/lib/node_modules/@stdlib/stats/incr/nanskewness/test/test.js b/lib/node_modules/@stdlib/stats/incr/nanskewness/test/test.js
new file mode 100644
index 000000000000..b276b10650d3
--- /dev/null
+++ b/lib/node_modules/@stdlib/stats/incr/nanskewness/test/test.js
@@ -0,0 +1,149 @@
+/**
+* @license Apache-2.0
+*
+* Copyright (c) 2020 The Stdlib Authors.
+*
+* Licensed under the Apache License, Version 2.0 (the "License");
+* you may not use this file except in compliance with the License.
+* You may obtain a copy of the License at
+*
+* http://www.apache.org/licenses/LICENSE-2.0
+*
+* Unless required by applicable law or agreed to in writing, software
+* distributed under the License is distributed on an "AS IS" BASIS,
+* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+* See the License for the specific language governing permissions and
+* limitations under the License.
+*/
+
+'use strict';
+
+// MODULES //
+
+var tape = require( 'tape' );
+var isnan = require( '@stdlib/math/base/assert/is-nan' );
+var abs = require( '@stdlib/math/base/special/abs' );
+var EPS = require( '@stdlib/constants/float64/eps' );
+var incrnanskewness = require( './../lib' );
+
+
+// TESTS //
+
+tape( 'main export is a function', function test( t ) {
+ t.ok( true, __filename );
+ t.strictEqual( typeof incrnanskewness, 'function', 'main export is a function' );
+ t.end();
+});
+
+tape( 'the function returns an accumulator function', function test( t ) {
+ t.equal( typeof incrnanskewness(), 'function', 'returns a function' );
+ t.end();
+});
+
+tape( 'the initial accumulated value is `null`', function test( t ) {
+ var acc = incrnanskewness();
+ t.equal( acc(), null, 'returns expected value' );
+ t.end();
+});
+
+tape( 'the accumulator function incrementally computes a corrected sample skewness', function test( t ) {
+ var expected;
+ var actual;
+ var delta;
+ var data;
+ var acc;
+ var tol;
+ var i;
+
+ data = [ 3.0, 2.0, 7.0, -1.0, 9.0 ];
+
+ // Check against the skewness function of the `e1071` R package:
+ expected = [
+ null,
+ null,
+ 1.457862967321305,
+ 0.4366620845757488,
+ 0.1171875
+ ];
+
+ acc = incrnanskewness();
+ for ( i = 0; i < data.length; i++ ) {
+ actual = acc( data[ i ] );
+ if ( expected[ i ] === null ) {
+ t.equal( actual, expected[i], 'returns null' );
+ } else {
+ delta = abs( actual - expected[ i ] );
+ tol = 1.5 * EPS * abs( expected[ i ] );
+ t.ok( delta <= tol, 'within tolerance. actual: '+actual+'. E: '+expected[i]+' Δ: '+delta+'. tol: '+tol );
+ }
+ }
+ t.end();
+});
+
+tape( 'if not provided an input value, the accumulator function returns the current corrected sample skewness', function test( t ) {
+ var expected;
+ var actual;
+ var delta;
+ var data;
+ var acc;
+ var tol;
+ var i;
+
+ data = [ 1.0, 4.0, 1.0, 0.0, 2.0, 12.0 ];
+ acc = incrnanskewness();
+ for ( i = 0; i < data.length; i++ ) {
+ acc( data[ i ] );
+ }
+ expected = 1.986829609590966;
+ actual = acc();
+ delta = abs( actual - expected );
+ tol = EPS * abs( expected );
+ t.ok( delta <= tol, 'within tolerance. actual: '+actual+'. E: '+expected+' Δ: '+delta+'. tol: '+tol );
+ t.end();
+});
+
+tape( 'the corrected sample skewness is `null` until at least 3 datums have been provided', function test( t ) {
+ var skewness;
+ var acc;
+
+ acc = incrnanskewness();
+
+ skewness = acc();
+ t.equal( skewness, null, 'returns null' );
+
+ skewness = acc( 2.0 );
+ t.equal( skewness, null, 'returns null' );
+
+ skewness = acc( 2.0 );
+ t.equal( skewness, null, 'returns null' );
+
+ skewness = acc( 3.0 );
+ t.notEqual( skewness, null, 'does not return null' );
+
+ t.end();
+});
+
+tape( 'if provided a `NaN`, the accumulator function ignores the `NaN` and returns current skewness', function test( t ) {
+ var data;
+ var nan = 2;
+ var acc;
+ var v;
+ var i;
+
+ data = [ NaN, 2.0, 1.0, -2.0, -3.0, 4.0, 5.0, 6.0, 7.0 ];
+ acc = incrnanskewness();
+ for ( i = 0; i < data.length; i++ ) {
+ v = acc( data[ i ] );
+ if ( isnan( data[i] ) ) {
+ t.equal( v, acc(), 'ignores NaN and returns current skewness' );
+ } else if ( nan > 0 ) {
+ t.equal( v, null, 'initial non NaN values are null' );
+ nan -= 1;
+ }
+ else {
+ t.equal( typeof v, 'number', 'returns a number' );
+ }
+ }
+
+ t.end();
+});