I reviewed the content of the `dataset_dict.py` file and identified the following typographical errors:

### Issue 1
```json
{
    "issue": "Typographical error in function docstring",
    "evidence": "Function applied on-the-fly on the examples when you iterate on the dataset",
    "description": "The docstring for the 'map' function contains the phrase 'Function applied on-the-fly on the examples when you iterate on the dataset'. It should be 'Function applied on-the-fly to the examples when you iterate on the dataset'. The correct preposition is 'to' instead of 'on'."
}
```

### Issue 2
```json
{
    "issue": "Typographical error in docstring example",
    "evidence": ">>> from datasets import load_dataset\n>>> ds = load_dataset('rotten_tomatoes', streaming=True)\n>>> ds['train'].features",
    "description": "In the example code within the docstring for the 'cast' function, single quotes are used inconsistently around dictionary keys and string values. For consistency and to follow Python conventions, double quotes should be used instead of single quotes. For example, 'label' should be \"label\" and 'text' should be \"text\"."
}
```

### Issue 3
```json
{
    "issue": "Typographical error in comment",
    "evidence": "# Function applied on-the-fly on the examples when iterating over the dataset.",
    "description": "In the comment preceding the 'map' function, the phrase 'on-the-fly on the examples' should be 'on-the-fly to the examples' to correct the preposition usage."
}
```

These issues highlight improper preposition use and inconsistent use of single and double quotes, which can be corrected to improve readability and adherence to standard Python conventions.