Add table unit tests...

.. also found and resolved some minor bugs (get(idx) batch length check should
be <=, various extern issues with UMD builds)

js/src/Arrow.externs.ts

@@ -54,6 +54,16 @@ Table.prototype.toString;
 Table.prototype.lengths;
 /** @type {?} */
 Table.prototype.batches;
+/** @type {?} */
+Table.prototype.countBy;
+/** @type {?} */
+Table.prototype.scan;
+/** @type {?} */
+Table.prototype.get;
+
+let CountByResult = function() {};
+/** @type {?} */
+CountByResult.prototype.asJSON;
 
 let Vector = function() {};
 /** @type {?} */

js/src/Arrow.ts

@@ -15,8 +15,8 @@
 // specific language governing permissions and limitations
 // under the License.
 
-import { Table, TableRow } from './table';
-import { lit, col } from './predicate';
+import { Table, TableRow, CountByResult } from './table';
+import { lit, col, Col, Value } from './predicate';
 import { Vector } from './vector/vector';
 import { Utf8Vector } from './vector/utf8';
 import { DictionaryVector } from './vector/dictionary';
@@ -54,8 +54,8 @@ Table['fromAsync'] = Table.fromAsync;
 BoolVector['pack'] = BoolVector.pack;
 
 export { read, readAsync };
-export { Table, TableRow };
-export { lit, col };
+export { Table, TableRow, CountByResult };
+export { lit, col, Col, Value };
 export { Vector, StructRow };
 export { Uint64, Int64, Int128 };
 export { NumericVectorConstructor } from './vector/numeric';
@@ -94,9 +94,11 @@ try {
         // string indexers tell closure compiler not to rename these properties
         Arrow['lit'] = lit;
         Arrow['col'] = col;
+        Arrow['Col'] = Col;
         Arrow['read'] = read;
-        Arrow['readAsync'] = readAsync;
+        Arrow['Value'] = Value;
         Arrow['Table'] = Table;
+        Arrow['readAsync'] = readAsync;
         Arrow['Vector'] = Vector;
         Arrow['StructRow'] = StructRow;
         Arrow['BoolVector'] = BoolVector;
@@ -120,6 +122,7 @@ try {
         Arrow['Float32Vector'] = Float32Vector;
         Arrow['Float64Vector'] = Float64Vector;
         Arrow['DecimalVector'] = DecimalVector;
+        Arrow['CountByResult'] = CountByResult;
         Arrow['TimestampVector'] = TimestampVector;
         Arrow['DictionaryVector'] = DictionaryVector;
         Arrow['FixedSizeListVector'] = FixedSizeListVector;

js/src/table.ts

@@ -42,7 +42,7 @@ export interface DataFrame {
     filter(predicate: Predicate): DataFrame;
     scan(next: NextFunc): void;
     count(): number;
-    countBy(col: (Col|string)): Table;
+    countBy(col: (Col|string)): CountByResult;
 }
 
 function columnsFromBatches(batches: Vector[][]) {
@@ -87,7 +87,7 @@ export class Table implements DataFrame {
     }
     get(idx: number): TableRow {
         let batch = 0;
-        while (idx > this.lengths[batch] && batch < this.lengths.length) {
+        while (idx >= this.lengths[batch] && batch < this.lengths.length) {
             idx -= this.lengths[batch++];
         }
 
@@ -114,7 +114,7 @@ export class Table implements DataFrame {
     count(): number {
         return this.lengths.reduce((acc, val) => acc + val);
     }
-    countBy(count_by: (Col|string)): Table {
+    countBy(count_by: (Col|string)): CountByResult {
         if (count_by instanceof String) {
             count_by = new Col(count_by);
         }
@@ -146,7 +146,7 @@ export class Table implements DataFrame {
             }
         }
 
-        return new Table({batches: [[keys, new Uint32Vector({data: counts})]]})
+        return new CountByResult(keys, new Uint32Vector({data: counts}))
     }
     *[Symbol.iterator]() {
         for (let batch = -1; ++batch < this.lengths.length;) {
@@ -215,7 +215,7 @@ class FilteredDataFrame implements DataFrame {
         );
     }
 
-    countBy(count_by: (Col|string)): Table {
+    countBy(count_by: (Col|string)): CountByResult {
         if (count_by instanceof String) {
             count_by = new Col(count_by);
         }
@@ -246,6 +246,22 @@ class FilteredDataFrame implements DataFrame {
             }
         }
 
-        return new Table({batches: [[keys, new Uint32Vector({data: counts})]]})
+        return new CountByResult(keys, new Uint32Vector({data: counts}))
+    }
+}
+
+export class CountByResult extends Table implements DataFrame {
+    constructor(readonly keys: Vector, readonly counts: Vector<number|null>) {
+        super({batches: [[keys, counts]]});
+    }
+
+    asJSON(): Object {
+        let result: {[key: string]: number|null} = {};
+
+        for (let i = -1; ++i < this.length;) {
+            result[this.keys.get(i)] = this.counts.get(i);
+        }
+
+        return result;
     }
 }