wikiann dataset is missing columns 
Hi @lhoestq 
thank you very much for the help, it would be very nice to have it included, here is the full code, one need to also convert tags to string first:

```
import datasets 
from datasets import load_dataset

def tags_to_spans(tags):
  """Convert tags to spans."""
  spans = set()
  span_start = 0
  span_end = 0
  active_conll_tag = None
  for index, string_tag in enumerate(tags):
    # Actual BIO tag.
    bio_tag = string_tag[0]
    assert bio_tag in ["B", "I", "O"], "Invalid Tag"
    conll_tag = string_tag[2:]
    if bio_tag == "O":
      # The span has ended.
      if active_conll_tag:
        spans.add((active_conll_tag, (span_start, span_end)))
      active_conll_tag = None
      # We don't care about tags we are
      # told to ignore, so we do nothing.
      continue
    elif bio_tag == "B":
      # We are entering a new span; reset indices and active tag to new span.
      if active_conll_tag:
        spans.add((active_conll_tag, (span_start, span_end)))
      active_conll_tag = conll_tag
      span_start = index
      span_end = index
    elif bio_tag == "I" and conll_tag == active_conll_tag:
      # We're inside a span.
      span_end += 1
    else:
      # This is the case the bio label is an "I", but either:
      # 1) the span hasn't started - i.e. an ill formed span.
      # 2) We have IOB1 tagging scheme.
      # We'll process the previous span if it exists, but also include this
      # span. This is important, because otherwise, a model may get a perfect
      # F1 score whilst still including false positive ill-formed spans.
      if active_conll_tag:
        spans.add((active_conll_tag, (span_start, span_end)))
      active_conll_tag = conll_tag
      span_start = index
      span_end = index
  # Last token might have been a part of a valid span.
  if active_conll_tag:
    spans.add((active_conll_tag, (span_start, span_end)))
  # Return sorted list of spans
  return sorted(list(spans), key=lambda x: x[1][0])

dataset = load_dataset('wikiann', 'en', split="train")
ner_tags = {
   0:"O",
   1:"B-PER",
   2:"I-PER",
   3:"B-ORG",
   4:"I-ORG",
   5:"B-LOC",
   6:"I-LOC"
}

def get_spans(tokens, tags):
  """Convert tags to textspans."""
  spans = tags_to_spans(tags)
  text_spans = [
      x[0] + ": " + " ".join([tokens[i]
                              for i in range(x[1][0], x[1][1] + 1)])
      for x in spans
  ]
  if not text_spans:
    text_spans = ["None"]
  return text_spans


for i, d in enumerate(dataset):
   tokens = d['tokens']
   tags = d['ner_tags']
   tags = [ner_tags[i] for i in tags]
   spans = get_spans(tokens, tags)
   print("spans ", spans)
   print(d)
   if i > 10:
     break; 
```
I am not sure how to contribute to the repository and how things work, could you let me know how one can access the datasets to be able to contribute to the repository? Maybe I could do it then
thanks 

Hi
Wikiann dataset needs to have "spans" columns, which is necessary to be able to use this dataset, but this column is missing from huggingface datasets, could you please have a look? thank you @lhoestq 
wikiann dataset is missing columns  
 Hi
Wikiann dataset needs to have "spans" columns, which is necessary to be able to use this dataset, but this column is missing from huggingface datasets, could you please have a look? thank you @lhoestq  
 Hi @lhoestq 
thank you very much for the help, it would be very nice to have it included, here is the full code, one need to also convert tags to string first:

```
import datasets 
from datasets import load_dataset

def tags_to_spans(tags):
  """Convert tags to spans."""
  spans = set()
  span_start = 0
  span_end = 0
  active_conll_tag = None
  for index, string_tag in enumerate(tags):
    # Actual BIO tag.
    bio_tag = string_tag[0]
    assert bio_tag in ["B", "I", "O"], "Invalid Tag"
    conll_tag = string_tag[2:]
    if bio_tag == "O":
      # The span has ended.
      if active_conll_tag:
        spans.add((active_conll_tag, (span_start, span_end)))
      active_conll_tag = None
      # We don't care about tags we are
      # told to ignore, so we do nothing.
      continue
    elif bio_tag == "B":
      # We are entering a new span; reset indices and active tag to new span.
      if active_conll_tag:
        spans.add((active_conll_tag, (span_start, span_end)))
      active_conll_tag = conll_tag
      span_start = index
      span_end = index
    elif bio_tag == "I" and conll_tag == active_conll_tag:
      # We're inside a span.
      span_end += 1
    else:
      # This is the case the bio label is an "I", but either:
      # 1) the span hasn't started - i.e. an ill formed span.
      # 2) We have IOB1 tagging scheme.
      # We'll process the previous span if it exists, but also include this
      # span. This is important, because otherwise, a model may get a perfect
      # F1 score whilst still including false positive ill-formed spans.
      if active_conll_tag:
        spans.add((active_conll_tag, (span_start, span_end)))
      active_conll_tag = conll_tag
      span_start = index
      span_end = index
  # Last token might have been a part of a valid span.
  if active_conll_tag:
    spans.add((active_conll_tag, (span_start, span_end)))
  # Return sorted list of spans
  return sorted(list(spans), key=lambda x: x[1][0])

dataset = load_dataset('wikiann', 'en', split="train")
ner_tags = {
   0:"O",
   1:"B-PER",
   2:"I-PER",
   3:"B-ORG",
   4:"I-ORG",
   5:"B-LOC",
   6:"I-LOC"
}

def get_spans(tokens, tags):
  """Convert tags to textspans."""
  spans = tags_to_spans(tags)
  text_spans = [
      x[0] + ": " + " ".join([tokens[i]
                              for i in range(x[1][0], x[1][1] + 1)])
      for x in spans
  ]
  if not text_spans:
    text_spans = ["None"]
  return text_spans


for i, d in enumerate(dataset):
   tokens = d['tokens']
   tags = d['ner_tags']
   tags = [ner_tags[i] for i in tags]
   spans = get_spans(tokens, tags)
   print("spans ", spans)
   print(d)
   if i > 10:
     break; 
```
I am not sure how to contribute to the repository and how things work, could you let me know how one can access the datasets to be able to contribute to the repository? Maybe I could do it then
thanks 
