def add_to_corpus_index(corpus_index,word,next_word):
    for el in corpus_index:
        if el[0]==word:
            el[1].append(next_word)
            return
        corpus_index.append([word,[next_word]])
def add_all_to_corpus_index(corpus_index,corpus):
    splitted_text=corpus.split()
    for i in range(len(splitted_text)-1):
        current_word,next_word=splitted_text[i],splitted_text[i+1]
        add_to_corpus_index(corpus_index,current_word,next_word)
corpus="Today is Sunday. I stay at home and keep coding. Today is Monday. I stay at office and keep cleaning. Today I stay awake."
corpus_index=[]
add_all_to_corpus_index(corpus_index, corpus)
print(corpus_index)