Merge pull request #195 from ashwin-sureshkumar/issue-91

docs(operators): add documentation for filter

src/operator-docs/filtering/filter.ts

@@ -1,6 +1,79 @@
 import { OperatorDoc } from '../operator.model';
 
 export const filter: OperatorDoc = {
-  'name': 'filter',
-  'operatorType': 'filtering'
+  name: 'filter',
+  operatorType: 'filtering',
+  signature:
+    'public filter(predicate: function(value: T, index: number): boolean, thisArg: any): Observable',
+  parameters: [
+    {
+      name: 'predicate',
+      type: 'function(value: T, index: number): boolean',
+      attribute: '',
+      description: `A function that evaluates each value emitted by the source Observable.
+         If it returns true, the value is emitted, if false the value is not passed to the output Observable.
+        The index parameter is the number i for the i-th source emission that has happened since the subscription,
+         starting from the number 0.`
+    },
+    {
+      name: 'thisArg',
+      type: 'any',
+      attribute: 'optional',
+      description:
+        'An optional argument to determine the value of this in the predicate function.'
+    }
+  ],
+  marbleUrl: 'http://reactivex.io/rxjs/img/filter.png',
+  shortDescription: {
+    description:
+      'Filter items emitted by the source Observable by only emitting those that satisfy a specified predicate.',
+    extras: [
+      {
+        type: 'Tip',
+        text: `
+        Like
+        <a
+         target="_blank"
+         href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/filter">
+          Array.prototype.filter()
+        </a>,
+        it only emits a value from the source if it passes a criterion function.
+        `
+      }
+    ]
+  },
+  walkthrough: {
+    description: `
+      <p>
+        Similar to the well-known <span class="markdown-code">Array.prototype.filter</span>
+         method, this operator takes values from the source Observable,
+         passes them through a predicate function and only emits those values that yielded true.
+      </p>
+    `
+  },
+  examples: [
+    {
+      name: 'Filter for even numbers',
+      code: `
+      //emit (1,2,3,4,5)
+      const source = Rx.Observable.from([1, 2, 3, 4, 5]);
+      //filter out non-even numbers
+      const example = source.filter(num => num % 2 === 0);
+      //output: "Even number: 2", "Even number: 4"
+      const subscribe = example.subscribe(val => console.log('Even number: ' + val));
+      `,
+      externalLink: {
+        platform: 'JSBin',
+        url: 'http://jsbin.com/vafogoluye/1/embed?js,console'
+      }
+    }
+  ],
+  relatedOperators: [
+    'distinct',
+    'distinctUntilChanged',
+    'distinctUntilKeyChanged',
+    'ignoreElements',
+    'partition',
+    'skip'
+  ]
 };