Issue: Can't get the text data when calling to_tf_dataset

I am working with the SST2 dataset, and am using TensorFlow 2.5
I'd like to convert it to a `tf.data.Dataset` by calling the `to_tf_dataset` method.
The following snippet is what I am using to achieve this:

```
from datasets import load_dataset
from transformers import DefaultDataCollator

data_collator = DefaultDataCollator(return_tensors="tf")
dataset = load_dataset("sst")

train_dataset = dataset["train"].to_tf_dataset(columns=['sentence'], label_cols="label", shuffle=True, batch_size=8,collate_fn=data_collator)
```
However, this only gets me the labels; the text--the most important part--is missing:

```
for s in train_dataset.take(1):
  print(s) #prints something like: ({}, <tf.Tensor: shape=(8,), ...>)
```

As you can see, it only returns the label part, not the data, as indicated by the empty dictionary, `{}`. So far, I've played with various settings of the method arguments, but to no avail; I do not want to perform any text processing at this time. On my quest to achieve what I want ( a `tf.data.Dataset`), I've consulted these resources:

[https://www.philschmid.de/huggingface-transformers-keras-tf](https://www.philschmid.de/huggingface-transformers-keras-tf)
[https://huggingface.co/docs/datasets/use_dataset.html?highlight=tensorflow](https://huggingface.co/docs/datasets/use_dataset.html?highlight=tensorflow)

I was surprised to not find more extensive examples on how to transform a Hugginface dataset to one compatible with TensorFlow.

If you could point me to where I am going wrong, please do so.
Thanks in advance for your support.

---
Edit: In the [docs](https://huggingface.co/docs/datasets/package_reference/main_classes.html#datasets.Dataset.to_tf_dataset), I found the following description:


_In general, only columns that the model can use as input should be included here (numeric data only)._

Does this imply that no textual, i.e., `string` data can be loaded?


Comments:
cc @Rocketknight1 

You are correct that `to_tf_dataset` only handles numerical columns right now, yes, though this is a limitation we might remove in future! The main reason we do this is that our models mostly do not include the tokenizer as a model layer, because it's very difficult to compile some of them in TF. So the "normal" Huggingface workflow is to first tokenize your dataset, and then pass tokenized tensors to the model.

For your use case, would you prefer to pass strings to the model, and use some text processing layers instead of the built-in tokenizers?

Also tagging @gante just so he's aware, but I can handle this one!

Thanks for the quick follow-up to my issue.

For my use-case, instead of the built-in tokenizers I wanted to use the `TextVectorization` layer to map from strings to integers. To achieve this, I came up with the following solution:

```
from datasets import load_dataset
from transformers import DefaultDataCollator
import tensorflow as tf
import string
import re
from tensorflow.keras.layers.experimental.preprocessing import TextVectorization

#some hyper-parameters for the text-to-integer mapping
max_features = 20000
embedding_dim = 128
sequence_length = 210

data_collator = DefaultDataCollator(return_tensors="tf")
dataset = load_dataset("sst", "default")

#adapt the vectorization layer on train data only
vectorize_layer.adapt(dataset["train"].to_dict(batched=False)["sentence"])

def prepare_features(text, label):
    text = tf.expand_dims(text, -1)
    return {"vectorized_text": vectorize_layer(text)[0], "label": tf.expand_dims(label, axis=-1)}

encoded_dataset = dataset.map(lambda example: prepare_features(example["sentence"], example["label"]), batched=False)


def custom_standardization(input_data):
    lowercase = tf.strings.lower(input_data)
    return tf.strings.regex_replace(
        lowercase, f"[{re.escape(string.punctuation)}]", ""
    )

vectorize_layer = TextVectorization(
    standardize=custom_standardization,
    max_tokens=max_features,
    output_mode="int",
    output_sequence_length=sequence_length,
)

train_dataset = encoded_dataset["train"].to_tf_dataset(columns=['vectorized_text'], label_cols=["label"],
                                                       shuffle=True, batch_size=1, collate_fn=data_collator).unbatch()
#similar for the other sub-sets

```

Since the strings would have been mapped to integers or floats at some point, it's no drawback that this mapping is done early in the process. 

For the future, however, it'd be more convenient to get the string data, since I am also inspecting the dataset (longest sentence, shortest sentence), which is more challenging when working with integer or float. For now, this can be done by calling `to_dict`.

> For the future, however, it'd be more convenient to get the string data, since I am also inspecting the dataset (longest sentence, shortest sentence), which is more challenging when working with integer or float.

Yes, I agree, so let's keep this issue open.

Going to close this now - methods like `to_tf_dataset` and `prepare_tf_dataset` now support string data, and have done for a while! If anyone sees this and is encountering issues with string data in those methods, please file a new issue!