Support decoding of tensors (#416)

* Support decoding of tensors (Closes #362)

* Remove debug line

src/tokenizers.js

@@ -122,6 +122,26 @@ function objectToMap(obj) {
     return new Map(Object.entries(obj));
 }
 
+/**
+ * Helper function to convert a tensor to a list before decoding.
+ * @param {Tensor} tensor The tensor to convert.
+ * @returns {number[]} The tensor as a list.
+ */
+function prepareTensorForDecode(tensor) {
+    const dims = tensor.dims;
+    switch (dims.length) {
+        case 1:
+            return tensor.tolist();
+        case 2:
+            if (dims[0] !== 1) {
+                throw new Error('Unable to decode tensor with `batch size !== 1`. Use `tokenizer.batch_decode(...)` for batched inputs.');
+            }
+            return tensor.tolist()[0];
+        default:
+            throw new Error(`Expected tensor to have 1-2 dimensions, got ${dims.length}.`)
+    }
+}
+
 /**
  * Clean up a list of simple English tokenization artifacts like spaces before punctuations and abbreviated forms
  * @param {string} text The text to clean up.
@@ -2556,18 +2576,21 @@ export class PreTrainedTokenizer extends Callable {
 
     /**
      * Decode a batch of tokenized sequences.
-     * @param {number[][]} batch List of tokenized input sequences.
+     * @param {number[][]|Tensor} batch List/Tensor of tokenized input sequences.
      * @param {Object} decode_args (Optional) Object with decoding arguments.
      * @returns {string[]} List of decoded sequences.
      */
     batch_decode(batch, decode_args = {}) {
+        if (batch instanceof Tensor) {
+            batch = batch.tolist();
+        }
         return batch.map(x => this.decode(x, decode_args));
     }
 
     /**
      * Decodes a sequence of token IDs back to a string.
      *
-     * @param {number[]} token_ids List of token IDs to decode.
+     * @param {number[]|Tensor} token_ids List/Tensor of token IDs to decode.
      * @param {Object} [decode_args={}]
      * @param {boolean} [decode_args.skip_special_tokens=false] If true, special tokens are removed from the output string.
      * @param {boolean} [decode_args.clean_up_tokenization_spaces=true] If true, spaces before punctuations and abbreviated forms are removed.
@@ -2579,6 +2602,10 @@ export class PreTrainedTokenizer extends Callable {
         token_ids,
         decode_args = {},
     ) {
+        if (token_ids instanceof Tensor) {
+            token_ids = prepareTensorForDecode(token_ids);
+        }
+
         if (!Array.isArray(token_ids) || token_ids.length === 0 || !isIntegralNumber(token_ids[0])) {
             throw Error("token_ids must be a non-empty array of integers.");
         }
@@ -3458,6 +3485,9 @@ export class WhisperTokenizer extends PreTrainedTokenizer {
         let text;
         // @ts-ignore
         if (decode_args && decode_args.decode_with_timestamps) {
+            if (token_ids instanceof Tensor) {
+                token_ids = prepareTensorForDecode(token_ids);
+            }
             text = this.decodeWithTimestamps(token_ids, decode_args);
         } else {
             text = super.decode(token_ids, decode_args);

tests/tokenizers.test.js

@@ -57,3 +57,27 @@ describe('Edge cases', () => {
         compare(token_ids, [101, 100, 102])
     }, 5000); // NOTE: 5 seconds
 });
+
+describe('Extra decoding tests', () => {
+    it('should be able to decode the output of encode', async () => {
+        let tokenizer = await AutoTokenizer.from_pretrained('Xenova/bert-base-uncased');
+
+        let text = 'hello world!';
+
+        // Ensure all the following outputs are the same:
+        // 1. Tensor of ids: allow decoding of 1D or 2D tensors.
+        let encodedTensor = tokenizer(text);
+        let decoded1 = tokenizer.decode(encodedTensor.input_ids, { skip_special_tokens: true });
+        let decoded2 = tokenizer.batch_decode(encodedTensor.input_ids, { skip_special_tokens: true })[0];
+        expect(decoded1).toEqual(text);
+        expect(decoded2).toEqual(text);
+
+        // 2. List of ids
+        let encodedList = tokenizer(text, { return_tensor: false });
+        let decoded3 = tokenizer.decode(encodedList.input_ids, { skip_special_tokens: true });
+        let decoded4 = tokenizer.batch_decode([encodedList.input_ids], { skip_special_tokens: true })[0];
+        expect(decoded3).toEqual(text);
+        expect(decoded4).toEqual(text);
+
+    }, MAX_TEST_EXECUTION_TIME);
+});