How to use the vaex.column._to_string_sequence function in vaex

def test_count_1d_strings():
    x = np.array([-1, -2, 0.5, 1.5, 4.5, 5], dtype='f8')
    y = x.astype(str).astype('O')
    y[2] = None
    y = vaex.column._to_string_sequence(y)
    bins = 5
    binner = vaex.superagg.BinnerScalar_float64('x', 0, 5, bins)
    binner.set_data(x)

    grid = vaex.superagg.Grid([binner])
    agg = vaex.superagg.AggCount_string(grid)
    agg.set_data(y, 0)
    agg_data = np.asarray(agg)
    grid.bin([agg])
    assert agg_data.tolist() == [0, 2, 0, 1, 0, 0, 1, 1]

1  very pretty
      2  is coming
      3  our
      4  6

    >>> df.text.str.isdigit()
    Expression = str_isdigit(text)
    Length: 5 dtype: bool (expression)
    ----------------------------------
    0  False
    1  False
    2  False
    3  False
    4   True
    """
    return _to_string_sequence(x).isdigit()

1  very pretty
      2  is coming
      3  our
      4  way.

    >>> df.text.str.title()
    Expression = str_title(text)
    Length: 5 dtype: str (expression)
    ---------------------------------
    0    Something
    1  Very Pretty
    2    Is Coming
    3          Our
    4         Way.
    """
    sl = _to_string_sequence(x).title()
    return column.ColumnStringArrow(sl.bytes, sl.indices, sl.length, sl.offset, string_sequence=sl)

1  very pretty
      2  is coming
      3  our
      4  way.

    >>> df.text.str.byte_length()
    Expression = str_byte_length(text)
    Length: 5 dtype: int64 (expression)
    -----------------------------------
    0   9
    1  11
    2   9
    3   3
    4   4
    """
    return _to_string_sequence(x).byte_length()

def check_array(x, dtype):
            if dtype == str_type:
                x = vaex.column._to_string_sequence(x)
            else:
                x = vaex.utils.as_contiguous(x)
                if x.dtype.kind in "mM":
                    # we pass datetime as int
                    x = x.view('uint64')
            return x
        block_map = {expr: block for expr, block in zip(self.expressions_all, blocks)}

1  very pretty
      2  is coming
      3  our
      4  way.

    >>> df.text.str.islower()
    Expression = str_islower(text)
    Length: 5 dtype: bool (expression)
    ----------------------------------
    0  False
    1   True
    2   True
    3   True
    4   True
    """
    return _to_string_sequence(x).islower()

1  very pretty
      2  is coming
      3  our
      4  way.

    >>> df.text.str.isalpha()
    Expression = str_isalpha(text)
    Length: 5 dtype: bool (expression)
    ----------------------------------
    0   True
    1  False
    2  False
    3   True
    4  False
    """
    return _to_string_sequence(x).isalpha()

1  very pretty
      2  is coming
      3  our
      4  way.

    >>> df.text.str.count(pat="et", regex=False)
    Expression = str_count(text, pat='et', regex=False)
    Length: 5 dtype: int64 (expression)
    -----------------------------------
    0  1
    1  1
    2  0
    3  0
    4  0
    """
    return _to_string_sequence(x).count(pat, regex)

4  True

    >>> df.text.str.equals('our')
    Expression = str_equals(text, 'our')
    Length: 5 dtype: bool (expression)
    ----------------------------------
    0  False
    1  False
    2  False
    3   True
    4  False
    """
    xmask = None
    ymask = None
    if not isinstance(x, six.string_types):
        x = _to_string_sequence(x)
    if not isinstance(y, six.string_types):
        y = _to_string_sequence(y)
    equals_mask = x.equals(y)
    return equals_mask

2  is coming
      3  our
      4  way.

    >>> df.text.str.rstrip(to_strip='ing')
    Expression = str_rstrip(text, to_strip='ing')
    Length: 5 dtype: str (expression)
    ---------------------------------
    0       Someth
    1  very pretty
    2       is com
    3          our
    4         way.
    """
    # in c++ we give empty string the same meaning as None
    sl = _to_string_sequence(x).rstrip('' if to_strip is None else to_strip) if to_strip != '' else x
    return column.ColumnStringArrow(sl.bytes, sl.indices, sl.length, sl.offset, string_sequence=sl)