Doc2vec '-' symbol occurrence
gensim's Phrases module may also be helpful:

from gensim.models import Phrases
documents = [
    "the mayor of new york was there",
    "machine learning can be useful sometimes",
    "new york mayor was present"
]

sentence_stream = [doc.split(" ") for doc in documents]

bigram = Phrases(sentence_stream, min_count=1, threshold=2)

sent = [u'the', u'mayor', u'of', u'new', u'york', u'was', u'there']
print(bigram[sent])
# Expected output:
# [u'the', u'mayor', u'of', u'new_york', u'was', u'there']


That code is from this other answer (I've copy-pasted it above for convenience).

For more on the Phrases module, check this page out.