Fix flatten implementation on objects (#7059)

BUG
Co-authored-by: Ping Yu <[email protected]>

Author: ahmedsabie

tfjs-core/src/util_base.ts

@@ -192,12 +192,26 @@ flatten<T extends number|boolean|string|Promise<number>|TypedArray>(
   if (result == null) {
     result = [];
   }
-  if (Array.isArray(arr) || isTypedArray(arr) && !skipTypedArray) {
+  if (typeof arr === 'boolean' || typeof arr === 'number' ||
+      typeof arr === 'string' || isPromise(arr) || arr == null ||
+      isTypedArray(arr) && skipTypedArray) {
+    result.push(arr as T);
+  } else if (Array.isArray(arr) || isTypedArray(arr)) {
     for (let i = 0; i < arr.length; ++i) {
       flatten(arr[i], result, skipTypedArray);
     }
   } else {
-    result.push(arr as T);
+    let maxIndex = -1;
+    for (const key of Object.keys(arr)) {
+      // 0 or positive integer.
+      if (/^([1-9]+[0-9]*|0)$/.test(key)) {
+        maxIndex = Math.max(maxIndex, Number(key));
+      }
+    }
+    for (let i = 0; i <= maxIndex; i++) {
+      // tslint:disable-next-line: no-unnecessary-type-assertion
+      flatten((arr as RecursiveArray<T>)[i], result, skipTypedArray);
+    }
   }
   return result;
 }

tfjs-core/src/util_test.ts

@@ -136,6 +136,11 @@ describe('Util', () => {
 });
 
 describe('util.flatten', () => {
+  it('empty', () => {
+    const data: number[] = [];
+    expect(util.flatten(data)).toEqual([]);
+  });
+
   it('nested number arrays', () => {
     expect(util.flatten([[1, 2, 3], [4, 5, 6]])).toEqual([1, 2, 3, 4, 5, 6]);
     expect(util.flatten([[[1, 2], [3, 4], [5, 6], [7, 8]]])).toEqual([
@@ -169,6 +174,20 @@ describe('util.flatten', () => {
       new Uint8Array([7, 8])
     ]);
   });
+
+  it('Int8Array', () => {
+    const data = [new Int8Array([1, 2])];
+    expect(util.flatten(data)).toEqual([1, 2]);
+  });
+
+  it('index signature', () => {
+    const data: {[index: number]: number} = {0: 1, 1: 2};
+    // Will be ignored since array iteration ignores negatives.
+    data[-1] = -1;
+    // Will be ignored since non-integer array keys are ignored.
+    data[3.2] = 4;
+    expect(util.flatten(data)).toEqual([1, 2]);
+  });
 });
 
 function encodeStrings(a: string[]): Uint8Array[] {