How can I store an array in a pandas dataframe?

I should store in the cell of a dataframe an array of strings, but the error is
ValueError: Must have equal len keys and value when setting with an iterable

I declared an array of words like this:
words = []
I have some text to extract words from and I put the words into the array.
for word in text:
words.append(word)

And I have a dataframe column declared like this:
dataframe['Words'] = ''

The error is triggered by:
dataframe.loc[x, 'Words'] = words

I should be able to store an array in a dataframe.

For example, if
text = 'Today is a sunny day'
I tokenize the sentence, and each token is a word.
I put each word in words
I would like the column Words of dataframe to be:
'Today', 'is', 'a', 'sunny', 'day'

What you want is not fully clear. In any case, assigning a list to a DataFrame's cell is not easy as a DataFrame is not designed to hold iterables. Pandas checks that the right-hand side of an assignment has the correct length, which doesn't work well with iterables like lists. In addition, you should rarely have to assign to single cells.

You can use a Series to force correct indexing:

text = 'Today is a sunny day'
words = text.split()
dataframe = pd.DataFrame(index=range(3), columns=['Words'])
x = 1
dataframe.loc[[x], 'Words'] = pd.Series([words], index=[x])

Output:

                        Words
0                         NaN
1  [Today, is, a, sunny, day]
2                         NaN

Note that the key x must be pre-existing, if this is not the case, a workaround might be to first assign a dummy value (e.g., NaN), then to assign the list.

x = 3
dataframe.loc[x, 'Words'] = np.nan
dataframe.loc[[x], 'Words'] = pd.Series([['A', 'B', 'C']], index=[x])

Output:

                        Words
0                         NaN
1  [Today, is, a, sunny, day]
2                         NaN
3                   [A, B, C]