Map function: Type error on iter #999
Hi, thanks for reporting.

It would be really helpful if you could provide the actual code of the `text_numbers_to_int` function so we can reproduce the error. ```
def text_numbers_to_int(text, column=""):
    """
    Convert text numbers to int.

    :param text: text numbers
    :return: int
    """
    try:
        numbers = find_numbers(text)
        if not numbers:
            return text
        result = ""
        i, j = 0, 0
        while i < len(text):
            if j < len(numbers) and i == numbers[j][1]:
                n = int(numbers[j][0]) if numbers[j][0] % 1 == 0 else float(numbers[j][0])
                result += str(n)
                i = numbers[j][2] #end
                j += 1
            else:
                result += text[i]
                i += 1
        if column:
            return{column: result}
        else:
            return {column: result}
    except Exception as e:
        print(e)
        return {column: result}
``` Maybe this is because of the `return text` line ? I think it should return a dictionary rather than a string Yes that was it, good catch! Thanks
## Describe the bug
Using the map function, it throws a type error on iter #999

Here is the code I am calling:
```
dataset = datasets.load_dataset('squad')
dataset['validation'].map(text_numbers_to_int, input_columns=['context'], fn_kwargs={'column': 'context'})
``` 
text_numbers_to_int returns the input text with numbers replaced in the format {'context': text}

It happens at 
`
File "C:\Users\lonek\anaconda3\envs\ai\Lib\site-packages\datasets\arrow_writer.py", line 289, in <listcomp>
    [row[0][col] for row in self.current_examples], type=col_type, try_type=col_try_type, col=col
`

The issue is that the list comprehension expects self.current_examples to be type tuple(dict, str), but for some reason 26 out of 1000 of the sefl.current_examples are type tuple(str, str)

Here is an example of what self.current_examples should be
({'context': 'Super Bowl 50 was an...merals 50.'}, '')

Here is an example of what self.current_examples are when it throws the error:
('The Panthers used th... Marriott.', '')
