docs: update examples

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---

Author: kgryte

lib/node_modules/@stdlib/ndarray/promotion-rules/README.md

@@ -97,28 +97,23 @@ var out = promotionRules( 'foo', 'generic' );
 <!-- eslint no-undef: "error" -->
 
 ```javascript
+var cartesianProduct = require( '@stdlib/array/cartesian-product' );
 var dtypes = require( '@stdlib/ndarray/dtypes' );
+var unzip = require( '@stdlib/utils/unzip' );
+var logEachMap = require( '@stdlib/console/log-each-map' );
 var promotionRules = require( '@stdlib/ndarray/promotion-rules' );
 
-var DTYPES;
-var dt1;
-var dt2;
-var dt;
-var i;
-var j;
-
 // Get the list of supported ndarray data types:
-DTYPES = dtypes();
-
-// Print the promotion rule for each pair of ndarray data types...
-for ( i = 0; i < DTYPES.length; i++ ) {
-    dt1 = DTYPES[ i ];
-    for ( j = 0; j < DTYPES.length; j++ ) {
-        dt2 = DTYPES[ j ];
-        dt = promotionRules( dt1, dt2 );
-        console.log( '(%s, %s) => %s', dt1, dt2, dt );
-    }
-}
+var dt = dtypes();
+
+// Generate a list of data type pairs:
+var pairs = cartesianProduct( dt, dt );
+
+// Split the pairs into separate arrays:
+var args = unzip( pairs );
+
+// Print the promotion rule for each pair of ndarray data types:
+logEachMap( '(%s, %s) => %s', args[ 0 ], args[ 1 ], promotionRules );
 ```
 
 </section>

lib/node_modules/@stdlib/ndarray/promotion-rules/examples/index.js

@@ -18,25 +18,20 @@
 
 'use strict';
 
+var cartesianProduct = require( '@stdlib/array/cartesian-product' );
 var dtypes = require( '@stdlib/ndarray/dtypes' );
+var unzip = require( '@stdlib/utils/unzip' );
+var logEachMap = require( '@stdlib/console/log-each-map' );
 var promotionRules = require( './../lib' );
 
-var DTYPES;
-var dt1;
-var dt2;
-var dt;
-var i;
-var j;
-
 // Get the list of supported ndarray data types:
-DTYPES = dtypes();
+var dt = dtypes();
+
+// Generate a list of data type pairs:
+var pairs = cartesianProduct( dt, dt );
+
+// Split the pairs into separate arrays:
+var args = unzip( pairs );
 
-// Print the promotion rule for each pair of ndarray data types...
-for ( i = 0; i < DTYPES.length; i++ ) {
-	dt1 = DTYPES[ i ];
-	for ( j = 0; j < DTYPES.length; j++ ) {
-		dt2 = DTYPES[ j ];
-		dt = promotionRules( dt1, dt2 );
-		console.log( '(%s, %s) => %s', dt1, dt2, dt );
-	}
-}
+// Print the promotion rule for each pair of ndarray data types:
+logEachMap( '(%s, %s) => %s', args[ 0 ], args[ 1 ], promotionRules );