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What's New in 0.24.0 (Month XX, 2018)

Warning

Starting January 1, 2019, pandas feature releases will support Python 3 only. See :ref:`install.dropping-27` for more.

{{ common_imports }}

These are the changes in pandas 0.24.0. See :ref:`release` for a full changelog including other versions of pandas.

New features

Accessing the values in a Series or Index

:attr:`Series.array` and :attr:`Index.array` have been added for extracting the array backing a Series or Index.

.. ipython:: python

   idx = pd.period_range('2000', periods=4)
   idx.array
   pd.Series(idx).array

Historically, this would have been done with series.values, but with .values it was unclear whether the returned value would be the actual array, some transformation of it, or one of pandas custom arrays (like Categorical). For example, with :class:`PeriodIndex`, .values generates a new ndarray of period objects each time.

.. ipython:: python

   id(idx.values)
   id(idx.values)

If you need an actual NumPy array, use :meth:`Series.to_numpy` or :meth:`Index.to_numpy`.

.. ipython:: python

   idx.to_numpy()
   pd.Series(idx).to_numpy()

For Series and Indexes backed by normal NumPy arrays, this will be the same thing (and the same as .values).

.. ipython:: python

   ser = pd.Series([1, 2, 3])
   ser.array
   ser.to_numpy()

We haven't removed or deprecated :attr:`Series.values` or :attr:`DataFrame.values`, but we recommend and using .array or .to_numpy() instead.

See :ref:`basics.dtypes` and :ref:`dsintro.attrs` for more.

ExtensionArray operator support

A Series based on an ExtensionArray now supports arithmetic and comparison operators (:issue:`19577`). There are two approaches for providing operator support for an ExtensionArray:

  1. Define each of the operators on your ExtensionArray subclass.
  2. Use an operator implementation from pandas that depends on operators that are already defined on the underlying elements (scalars) of the ExtensionArray.

See the :ref:`ExtensionArray Operator Support <extending.extension.operator>` documentation section for details on both ways of adding operator support.

Optional Integer NA Support

Pandas has gained the ability to hold integer dtypes with missing values. This long requested feature is enabled through the use of :ref:`extension types <extending.extension-types>`. Here is an example of the usage.

We can construct a Series with the specified dtype. The dtype string Int64 is a pandas ExtensionDtype. Specifying a list or array using the traditional missing value marker of np.nan will infer to integer dtype. The display of the Series will also use the NaN to indicate missing values in string outputs. (:issue:`20700`, :issue:`20747`, :issue:`22441`, :issue:`21789`, :issue:`22346`)

.. ipython:: python

   s = pd.Series([1, 2, np.nan], dtype='Int64')
   s

Operations on these dtypes will propagate NaN as other pandas operations.

.. ipython:: python

   # arithmetic
   s + 1

   # comparison
   s == 1

   # indexing
   s.iloc[1:3]

   # operate with other dtypes
   s + s.iloc[1:3].astype('Int8')

   # coerce when needed
   s + 0.01

These dtypes can operate as part of of DataFrame.

.. ipython:: python

   df = pd.DataFrame({'A': s, 'B': [1, 1, 3], 'C': list('aab')})
   df
   df.dtypes

These dtypes can be merged & reshaped & casted.

.. ipython:: python

   pd.concat([df[['A']], df[['B', 'C']]], axis=1).dtypes
   df['A'].astype(float)

Reduction and groupby operations such as 'sum' work.

.. ipython:: python

   df.sum()
   df.groupby('B').A.sum()

Warning

The Integer NA support currently uses the captilized dtype version, e.g. Int8 as compared to the traditional int8. This may be changed at a future date.

read_html Enhancements

:func:`read_html` previously ignored colspan and rowspan attributes. Now it understands them, treating them as sequences of cells with the same value. (:issue:`17054`)

.. ipython:: python

    result = pd.read_html("""
      <table>
        <thead>
          <tr>
            <th>A</th><th>B</th><th>C</th>
          </tr>
        </thead>
        <tbody>
          <tr>
            <td colspan="2">1</td><td>2</td>
          </tr>
        </tbody>
      </table>""")

Previous Behavior:

In [13]: result
Out [13]:
[   A  B   C
 0  1  2 NaN]

Current Behavior:

.. ipython:: python

    result

Storing Interval and Period Data in Series and DataFrame

Interval and Period data may now be stored in a Series or DataFrame, in addition to an :class:`IntervalIndex` and :class:`PeriodIndex` like previously (:issue:`19453`, :issue:`22862`).

.. ipython:: python

   ser = pd.Series(pd.interval_range(0, 5))
   ser
   ser.dtype

And for periods:

.. ipython:: python

   pser = pd.Series(pd.date_range("2000", freq="D", periods=5))
   pser
   pser.dtype

Previously, these would be cast to a NumPy array with object dtype. In general, this should result in better performance when storing an array of intervals or periods in a :class:`Series` or column of a :class:`DataFrame`.

Note that the .values of a Series containing one of these types is no longer a NumPy array, but rather an ExtensionArray:

.. ipython:: python

   ser.values
   pser.values

This is the same behavior as Series.values for categorical data. See :ref:`whatsnew_0240.api_breaking.interval_values` for more.

New Styler.pipe() method

The :class:`~pandas.io.formats.style.Styler` class has gained a :meth:`~pandas.io.formats.style.Styler.pipe` method (:issue:`23229`). This provides a convenient way to apply users' predefined styling functions, and can help reduce "boilerplate" when using DataFrame styling functionality repeatedly within a notebook.

.. ipython:: python

    df = pandas.DataFrame({'N': [1250, 1500, 1750], 'X': [0.25, 0.35, 0.50]})

    def format_and_align(styler):
        return (styler.format({'N': '{:,}', 'X': '{:.1%}'})
                      .set_properties(**{'text-align': 'right'}))

    df.style.pipe(format_and_align).set_caption('Summary of results.')

Similar methods already exist for other classes in pandas, including :meth:`DataFrame.pipe`, :meth:`Groupby.pipe`, and :meth:`Resampler.pipe`.

Joining with two multi-indexes

:func:`Datafame.merge` and :func:`Dataframe.join` can now be used to join multi-indexed Dataframe instances on the overlaping index levels (:issue:`6360`)

See the :ref:`Merge, join, and concatenate <merging.Join_with_two_multi_indexes>` documentation section.

.. ipython:: python

   index_left = pd.MultiIndex.from_tuples([('K0', 'X0'), ('K0', 'X1'),
                                          ('K1', 'X2')],
                                          names=['key', 'X'])


   left = pd.DataFrame({'A': ['A0', 'A1', 'A2'],
                        'B': ['B0', 'B1', 'B2']},
                         index=index_left)


   index_right = pd.MultiIndex.from_tuples([('K0', 'Y0'), ('K1', 'Y1'),
                                           ('K2', 'Y2'), ('K2', 'Y3')],
                                           names=['key', 'Y'])


   right = pd.DataFrame({'C': ['C0', 'C1', 'C2', 'C3'],
                         'D': ['D0', 'D1', 'D2', 'D3']},
                        index=index_right)


    left.join(right)

For earlier versions this can be done using the following.

.. ipython:: python

   pd.merge(left.reset_index(), right.reset_index(),
            on=['key'], how='inner').set_index(['key', 'X', 'Y'])

Renaming names in a MultiIndex

:func:`DataFrame.rename_axis` now supports index and columns arguments and :func:`Series.rename_axis` supports index argument (:issue:`19978`)

This change allows a dictionary to be passed so that some of the names of a MultiIndex can be changed.

Example:

.. ipython:: python

    mi = pd.MultiIndex.from_product([list('AB'), list('CD'), list('EF')],
                                    names=['AB', 'CD', 'EF'])
    df = pd.DataFrame([i for i in range(len(mi))], index=mi, columns=['N'])
    df
    df.rename_axis(index={'CD': 'New'})

See the :ref:`advanced docs on renaming<advanced.index_names>` for more details.

Other Enhancements

Backwards incompatible API changes

Dependencies have increased minimum versions

We have updated our minimum supported versions of dependencies (:issue:`21242`, :issue:`18742`, :issue:`23774`). If installed, we now require:

Package Minimum Version Required
numpy 1.12.0 X
bottleneck 1.2.0  
fastparquet 0.1.2  
matplotlib 2.0.0  
numexpr 2.6.1  
pandas-gbq 0.8.0  
pyarrow 0.7.0  
pytables 3.4.2  
scipy 0.18.1  
xlrd 1.0.0  

Additionally we no longer depend on feather-format for feather based storage and replaced it with references to pyarrow (:issue:`21639` and :issue:`23053`).

os.linesep is used for line_terminator of DataFrame.to_csv

:func:`DataFrame.to_csv` now uses :func:`os.linesep` rather than '\n' for the default line terminator (:issue:`20353`). This change only affects when running on Windows, where '\r\n' was used for line terminator even when '\n' was passed in line_terminator.

Previous Behavior on Windows:

In [1]: data = pd.DataFrame({
...:     "string_with_lf": ["a\nbc"],
...:     "string_with_crlf": ["a\r\nbc"]
...: })

In [2]: # When passing file PATH to to_csv, line_terminator does not work, and csv is saved with '\r\n'.
...: # Also, this converts all '\n's in the data to '\r\n'.
...: data.to_csv("test.csv", index=False, line_terminator='\n')

In [3]: with open("test.csv", mode='rb') as f:
...:     print(f.read())
b'string_with_lf,string_with_crlf\r\n"a\r\nbc","a\r\r\nbc"\r\n'

In [4]: # When passing file OBJECT with newline option to to_csv, line_terminator works.
...: with open("test2.csv", mode='w', newline='\n') as f:
...:     data.to_csv(f, index=False, line_terminator='\n')

In [5]: with open("test2.csv", mode='rb') as f:
...:     print(f.read())
b'string_with_lf,string_with_crlf\n"a\nbc","a\r\nbc"\n'

New Behavior on Windows:

  • By passing line_terminator explicitly, line terminator is set to that character.

  • The value of line_terminator only affects the line terminator of CSV, so it does not change the value inside the data.

    In [1]: data = pd.DataFrame({
...:     "string_with_lf": ["a\nbc"],
...:     "string_with_crlf": ["a\r\nbc"]
...: })

In [2]: data.to_csv("test.csv", index=False, line_terminator='\n')

In [3]: with open("test.csv", mode='rb') as f:
...:     print(f.read())
b'string_with_lf,string_with_crlf\n"a\nbc","a\r\nbc"\n'

  • On Windows, the value of os.linesep is '\r\n', so if line_terminator is not set, '\r\n' is used for line terminator.

  • Again, it does not affect the value inside the data.

    In [1]: data = pd.DataFrame({
...: "string_with_lf": ["a\nbc"],
...: "string_with_crlf": ["a\r\nbc"]
...: })

In [2]: data.to_csv("test.csv", index=False)

In [3]: with open("test.csv", mode='rb') as f:
...:     print(f.read())
b'string_with_lf,string_with_crlf\r\n"a\nbc","a\r\nbc"\r\n'

  • For files objects, specifying newline is not sufficient to set the line terminator. You must pass in the line_terminator explicitly, even in this case.

    In [1]: data = pd.DataFrame({
...: "string_with_lf": ["a\nbc"],
...: "string_with_crlf": ["a\r\nbc"]
...: })

In [2]: with open("test2.csv", mode='w', newline='\n') as f:
...:     data.to_csv(f, index=False)

In [3]: with open("test2.csv", mode='rb') as f:
...:     print(f.read())
b'string_with_lf,string_with_crlf\r\n"a\nbc","a\r\nbc"\r\n'

IntervalIndex.values is now an IntervalArray

The :attr:`~Interval.values` attribute of an :class:`IntervalIndex` now returns an IntervalArray, rather than a NumPy array of :class:`Interval` objects (:issue:`19453`).

Previous Behavior:

In [1]: idx = pd.interval_range(0, 4)

In [2]: idx.values
Out[2]:
array([Interval(0, 1, closed='right'), Interval(1, 2, closed='right'),
       Interval(2, 3, closed='right'), Interval(3, 4, closed='right')],
      dtype=object)

New Behavior:

.. ipython:: python

   idx = pd.interval_range(0, 4)
   idx.values

This mirrors CategoricalIndex.values, which returns a Categorical.

For situations where you need an ndarray of Interval objects, use :meth:`numpy.asarray`.

.. ipython:: python

   np.asarray(idx)
   idx.values.astype(object)

Parsing Datetime Strings with Timezone Offsets

Previously, parsing datetime strings with UTC offsets with :func:`to_datetime` or :class:`DatetimeIndex` would automatically convert the datetime to UTC without timezone localization. This is inconsistent from parsing the same datetime string with :class:`Timestamp` which would preserve the UTC offset in the tz attribute. Now, :func:`to_datetime` preserves the UTC offset in the tz attribute when all the datetime strings have the same UTC offset (:issue:`17697`, :issue:`11736`, :issue:`22457`)

Previous Behavior:

In [2]: pd.to_datetime("2015-11-18 15:30:00+05:30")
Out[2]: Timestamp('2015-11-18 10:00:00')

In [3]: pd.Timestamp("2015-11-18 15:30:00+05:30")
Out[3]: Timestamp('2015-11-18 15:30:00+0530', tz='pytz.FixedOffset(330)')

# Different UTC offsets would automatically convert the datetimes to UTC (without a UTC timezone)
In [4]: pd.to_datetime(["2015-11-18 15:30:00+05:30", "2015-11-18 16:30:00+06:30"])
Out[4]: DatetimeIndex(['2015-11-18 10:00:00', '2015-11-18 10:00:00'], dtype='datetime64[ns]', freq=None)

Current Behavior:

.. ipython:: python

    pd.to_datetime("2015-11-18 15:30:00+05:30")
    pd.Timestamp("2015-11-18 15:30:00+05:30")

Parsing datetime strings with the same UTC offset will preserve the UTC offset in the tz

.. ipython:: python

    pd.to_datetime(["2015-11-18 15:30:00+05:30"] * 2)

Parsing datetime strings with different UTC offsets will now create an Index of datetime.datetime objects with different UTC offsets

.. ipython:: python

    idx = pd.to_datetime(["2015-11-18 15:30:00+05:30", "2015-11-18 16:30:00+06:30"])
    idx
    idx[0]
    idx[1]

Passing utc=True will mimic the previous behavior but will correctly indicate that the dates have been converted to UTC

.. ipython:: python

    pd.to_datetime(["2015-11-18 15:30:00+05:30", "2015-11-18 16:30:00+06:30"], utc=True)

CalendarDay Offset

:class:`Day` and associated frequency alias 'D' were documented to represent a calendar day; however, arithmetic and operations with :class:`Day` sometimes respected absolute time instead (i.e. Day(n) and acted identically to Timedelta(days=n)).

Previous Behavior:

In [2]: ts = pd.Timestamp('2016-10-30 00:00:00', tz='Europe/Helsinki')

# Respects calendar arithmetic
In [3]: pd.date_range(start=ts, freq='D', periods=3)
Out[3]:
DatetimeIndex(['2016-10-30 00:00:00+03:00', '2016-10-31 00:00:00+02:00',
               '2016-11-01 00:00:00+02:00'],
              dtype='datetime64[ns, Europe/Helsinki]', freq='D')

# Respects absolute arithmetic
In [4]: ts + pd.tseries.frequencies.to_offset('D')
Out[4]: Timestamp('2016-10-30 23:00:00+0200', tz='Europe/Helsinki')

:class:`CalendarDay` and associated frequency alias 'CD' are now available and respect calendar day arithmetic while :class:`Day` and frequency alias 'D' will now respect absolute time (:issue:`22274`, :issue:`20596`, :issue:`16980`, :issue:`8774`) See the :ref:`documentation here <timeseries.dayvscalendarday>` for more information.

Addition with :class:`CalendarDay` across a daylight savings time transition:

.. ipython:: python

   ts = pd.Timestamp('2016-10-30 00:00:00', tz='Europe/Helsinki')
   ts + pd.offsets.Day(1)
   ts + pd.offsets.CalendarDay(1)

Time values in dt.end_time and to_timestamp(how='end')

The time values in :class:`Period` and :class:`PeriodIndex` objects are now set to '23:59:59.999999999' when calling :attr:`Series.dt.end_time`, :attr:`Period.end_time`, :attr:`PeriodIndex.end_time`, :func:`Period.to_timestamp()` with how='end', or :func:`PeriodIndex.to_timestamp()` with how='end' (:issue:`17157`)

Previous Behavior:

In [2]: p = pd.Period('2017-01-01', 'D')
In [3]: pi = pd.PeriodIndex([p])

In [4]: pd.Series(pi).dt.end_time[0]
Out[4]: Timestamp(2017-01-01 00:00:00)

In [5]: p.end_time
Out[5]: Timestamp(2017-01-01 23:59:59.999999999)

Current Behavior:

Calling :attr:`Series.dt.end_time` will now result in a time of '23:59:59.999999999' as is the case with :attr:`Period.end_time`, for example

.. ipython:: python

   p = pd.Period('2017-01-01', 'D')
   pi = pd.PeriodIndex([p])

   pd.Series(pi).dt.end_time[0]

   p.end_time

Sparse Data Structure Refactor

SparseArray, the array backing SparseSeries and the columns in a SparseDataFrame, is now an extension array (:issue:`21978`, :issue:`19056`, :issue:`22835`). To conform to this interface and for consistency with the rest of pandas, some API breaking changes were made:

  • SparseArray is no longer a subclass of :class:`numpy.ndarray`. To convert a SparseArray to a NumPy array, use :meth:`numpy.asarray`.
  • SparseArray.dtype and SparseSeries.dtype are now instances of :class:`SparseDtype`, rather than np.dtype. Access the underlying dtype with SparseDtype.subtype.
  • :meth:`numpy.asarray(sparse_array)` now returns a dense array with all the values, not just the non-fill-value values (:issue:`14167`)
  • SparseArray.take now matches the API of :meth:`pandas.api.extensions.ExtensionArray.take` (:issue:`19506`):
    • The default value of allow_fill has changed from False to True.
    • The out and mode parameters are now longer accepted (previously, this raised if they were specified).
    • Passing a scalar for indices is no longer allowed.
  • The result of concatenating a mix of sparse and dense Series is a Series with sparse values, rather than a SparseSeries.
  • SparseDataFrame.combine and DataFrame.combine_first no longer supports combining a sparse column with a dense column while preserving the sparse subtype. The result will be an object-dtype SparseArray.
  • Setting :attr:`SparseArray.fill_value` to a fill value with a different dtype is now allowed.
  • DataFrame[column] is now a :class:`Series` with sparse values, rather than a :class:`SparseSeries`, when slicing a single column with sparse values (:issue:`23559`).

Some new warnings are issued for operations that require or are likely to materialize a large dense array:

  • A :class:`errors.PerformanceWarning` is issued when using fillna with a method, as a dense array is constructed to create the filled array. Filling with a value is the efficient way to fill a sparse array.
  • A :class:`errors.PerformanceWarning` is now issued when concatenating sparse Series with differing fill values. The fill value from the first sparse array continues to be used.

In addition to these API breaking changes, many :ref:`performance improvements and bug fixes have been made <whatsnew_0240.bug_fixes.sparse>`.

Finally, a Series.sparse accessor was added to provide sparse-specific methods like :meth:`Series.sparse.from_coo`.

.. ipython:: python

   s = pd.Series([0, 0, 1, 1, 1], dtype='Sparse[int]')
   s.sparse.density

Raise ValueError in DataFrame.to_dict(orient='index')

Bug in :func:`DataFrame.to_dict` raises ValueError when used with orient='index' and a non-unique index instead of losing data (:issue:`22801`)

.. ipython:: python
    :okexcept:

    df = pd.DataFrame({'a': [1, 2], 'b': [0.5, 0.75]}, index=['A', 'A'])
    df

    df.to_dict(orient='index')

Tick DateOffset Normalize Restrictions

Creating a Tick object (:class:`Day`, :class:`Hour`, :class:`Minute`, :class:`Second`, :class:`Milli`, :class:`Micro`, :class:`Nano`) with normalize=True is no longer supported. This prevents unexpected behavior where addition could fail to be monotone or associative. (:issue:`21427`)

Previous Behavior:

In [2]: ts = pd.Timestamp('2018-06-11 18:01:14')

In [3]: ts
Out[3]: Timestamp('2018-06-11 18:01:14')

In [4]: tic = pd.offsets.Hour(n=2, normalize=True)
   ...:

In [5]: tic
Out[5]: <2 * Hours>

In [6]: ts + tic
Out[6]: Timestamp('2018-06-11 00:00:00')

In [7]: ts + tic + tic + tic == ts + (tic + tic + tic)
Out[7]: False

Current Behavior:

.. ipython:: python

    ts = pd.Timestamp('2018-06-11 18:01:14')
    tic = pd.offsets.Hour(n=2)
    ts + tic + tic + tic == ts + (tic + tic + tic)

Period Subtraction

Subtraction of a Period from another Period will give a DateOffset. instead of an integer (:issue:`21314`)

.. ipython:: python

    june = pd.Period('June 2018')
    april = pd.Period('April 2018')
    june - april

Previous Behavior:

In [2]: june = pd.Period('June 2018')

In [3]: april = pd.Period('April 2018')

In [4]: june - april
Out [4]: 2

Similarly, subtraction of a Period from a PeriodIndex will now return an Index of DateOffset objects instead of an Int64Index

.. ipython:: python

    pi = pd.period_range('June 2018', freq='M', periods=3)
    pi - pi[0]

Previous Behavior:

In [2]: pi = pd.period_range('June 2018', freq='M', periods=3)

In [3]: pi - pi[0]
Out[3]: Int64Index([0, 1, 2], dtype='int64')

Addition/Subtraction of NaN from :class:`DataFrame`

Adding or subtracting NaN from a :class:`DataFrame` column with timedelta64[ns] dtype will now raise a TypeError instead of returning all-NaT. This is for compatibility with TimedeltaIndex and Series behavior (:issue:`22163`)

.. ipython:: python
   :okexcept:

   df = pd.DataFrame([pd.Timedelta(days=1)])
   df - np.nan

Previous Behavior:

In [4]: df = pd.DataFrame([pd.Timedelta(days=1)])

In [5]: df - np.nan
Out[5]:
    0
0 NaT

DataFrame Comparison Operations Broadcasting Changes

Previously, the broadcasting behavior of :class:`DataFrame` comparison operations (==, !=, ...) was inconsistent with the behavior of arithmetic operations (+, -, ...). The behavior of the comparison operations has been changed to match the arithmetic operations in these cases. (:issue:`22880`)

The affected cases are:

  • operating against a 2-dimensional np.ndarray with either 1 row or 1 column will now broadcast the same way a np.ndarray would (:issue:`23000`).
  • a list or tuple with length matching the number of rows in the :class:`DataFrame` will now raise ValueError instead of operating column-by-column (:issue:`22880`.
  • a list or tuple with length matching the number of columns in the :class:`DataFrame` will now operate row-by-row instead of raising ValueError (:issue:`22880`).

Previous Behavior:

In [3]: arr = np.arange(6).reshape(3, 2)
In [4]: df = pd.DataFrame(arr)

In [5]: df == arr[[0], :]
   ...: # comparison previously broadcast where arithmetic would raise
Out[5]:
       0      1
0   True   True
1  False  False
2  False  False
In [6]: df + arr[[0], :]
...
ValueError: Unable to coerce to DataFrame, shape must be (3, 2): given (1, 2)

In [7]: df == (1, 2)
   ...: # length matches number of columns;
   ...: # comparison previously raised where arithmetic would broadcast
...
ValueError: Invalid broadcasting comparison [(1, 2)] with block values
In [8]: df + (1, 2)
Out[8]:
   0  1
0  1  3
1  3  5
2  5  7

In [9]: df == (1, 2, 3)
   ...: # length matches number of rows
   ...: # comparison previously broadcast where arithmetic would raise
Out[9]:
       0      1
0  False   True
1   True  False
2  False  False
In [10]: df + (1, 2, 3)
...
ValueError: Unable to coerce to Series, length must be 2: given 3

Current Behavior:

.. ipython:: python
   :okexcept:

   arr = np.arange(6).reshape(3, 2)
   df = pd.DataFrame(arr)


.. ipython:: python

   # Comparison operations and arithmetic operations both broadcast.
   df == arr[[0], :]
   df + arr[[0], :]


.. ipython:: python

   # Comparison operations and arithmetic operations both broadcast.
   df == (1, 2)
   df + (1, 2)


.. ipython:: python
   :okexcept:

   # Comparison operations and arithmetic opeartions both raise ValueError.
   df == (1, 2, 3)
   df + (1, 2, 3)

DataFrame Arithmetic Operations Broadcasting Changes

:class:`DataFrame` arithmetic operations when operating with 2-dimensional np.ndarray objects now broadcast in the same way as np.ndarray broadcast. (:issue:`23000`)

Previous Behavior:

In [3]: arr = np.arange(6).reshape(3, 2)
In [4]: df = pd.DataFrame(arr)
In [5]: df + arr[[0], :]   # 1 row, 2 columns
...
ValueError: Unable to coerce to DataFrame, shape must be (3, 2): given (1, 2)
In [6]: df + arr[:, [1]]   # 1 column, 3 rows
...
ValueError: Unable to coerce to DataFrame, shape must be (3, 2): given (3, 1)

Current Behavior:

.. ipython:: python

   arr = np.arange(6).reshape(3, 2)
   df = pd.DataFrame(arr)
   df


.. ipython:: python

   df + arr[[0], :]   # 1 row, 2 columns
   df + arr[:, [1]]   # 1 column, 3 rows

ExtensionType Changes

:class:`pandas.api.extensions.ExtensionDtype` Equality and Hashability

Pandas now requires that extension dtypes be hashable. The base class implements a default __eq__ and __hash__. If you have a parametrized dtype, you should update the ExtensionDtype._metadata tuple to match the signature of your __init__ method. See :class:`pandas.api.extensions.ExtensionDtype` for more (:issue:`22476`).

Other changes

Series and Index Data-Dtype Incompatibilities

Series and Index constructors now raise when the data is incompatible with a passed dtype= (:issue:`15832`)

Previous Behavior:

In [4]: pd.Series([-1], dtype="uint64")
Out [4]:
0    18446744073709551615
dtype: uint64

Current Behavior:

In [4]: pd.Series([-1], dtype="uint64")
Out [4]:
...
OverflowError: Trying to coerce negative values to unsigned integers

Crosstab Preserves Dtypes

:func:`crosstab` will preserve now dtypes in some cases that previously would cast from integer dtype to floating dtype (:issue:`22019`)

Previous Behavior:

In [3]: df = pd.DataFrame({'a': [1, 2, 2, 2, 2], 'b': [3, 3, 4, 4, 4],
   ...:                    'c': [1, 1, np.nan, 1, 1]})
In [4]: pd.crosstab(df.a, df.b, normalize='columns')
Out[4]:
b    3    4
a
1  0.5  0.0
2  0.5  1.0

Current Behavior:

In [3]: df = pd.DataFrame({'a': [1, 2, 2, 2, 2], 'b': [3, 3, 4, 4, 4],
   ...:                    'c': [1, 1, np.nan, 1, 1]})
In [4]: pd.crosstab(df.a, df.b, normalize='columns')

Datetimelike API Changes

Other API Changes

Deprecations

Integer Addition/Subtraction with Datetime-like Classes Is Deprecated

In the past, users could add or subtract integers or integer-dtypes arrays from :class:`Period`, :class:`PeriodIndex`, and in some cases :class:`Timestamp`, :class:`DatetimeIndex` and :class:`TimedeltaIndex`.

This usage is now deprecated. Instead add or subtract integer multiples of the object's freq attribute (:issue:`21939`)

Previous Behavior:

In [3]: per = pd.Period('2016Q1')
In [4]: per + 3
Out[4]: Period('2016Q4', 'Q-DEC')

In [5]: ts = pd.Timestamp('1994-05-06 12:15:16', freq=pd.offsets.Hour())
In [6]: ts + 2
Out[6]: Timestamp('1994-05-06 14:15:16', freq='H')

In [7]: tdi = pd.timedelta_range('1D', periods=2)
In [8]: tdi - np.array([2, 1])
Out[8]: TimedeltaIndex(['-1 days', '1 days'], dtype='timedelta64[ns]', freq=None)

In [9]: dti = pd.date_range('2001-01-01', periods=2, freq='7D')
In [10]: dti + pd.Index([1, 2])
Out[10]: DatetimeIndex(['2001-01-08', '2001-01-22'], dtype='datetime64[ns]', freq=None)

Current Behavior:

.. ipython:: python
    :okwarning:

    per = pd.Period('2016Q1')
    per + 3

    per = pd.Period('2016Q1')
    per + 3 * per.freq

    ts = pd.Timestamp('1994-05-06 12:15:16', freq=pd.offsets.Hour())
    ts + 2 * ts.freq

    tdi = pd.timedelta_range('1D', periods=2)
    tdi - np.array([2 * tdi.freq, 1 * tdi.freq])

    dti = pd.date_range('2001-01-01', periods=2, freq='7D')
    dti + pd.Index([1 * dti.freq, 2 * dti.freq])

Removal of prior version deprecations/changes

Performance Improvements

Documentation Changes

  • Added sphinx spelling extension, updated documentation on how to use the spell check (:issue:`21079`)

Bug Fixes

Categorical

Datetimelike

Timedelta

Timezones

Offsets

Numeric

Strings

Interval

Indexing

Missing

MultiIndex

I/O

Proper handling of np.NaN in a string data-typed column with the Python engine

There was bug in :func:`read_excel` and :func:`read_csv` with the Python engine, where missing values turned to 'nan' with dtype=str and na_filter=True. Now, these missing values are converted to the string missing indicator, np.nan. (:issue 20377)

.. ipython:: python
   :suppress:

   from pandas.compat import StringIO

Previous Behavior:

In [5]: data = 'a,b,c\n1,,3\n4,5,6'
In [6]: df = pd.read_csv(StringIO(data), engine='python', dtype=str, na_filter=True)
In [7]: df.loc[0, 'b']
Out[7]:
'nan'

Current Behavior:

.. ipython:: python

   data = 'a,b,c\n1,,3\n4,5,6'
   df = pd.read_csv(StringIO(data), engine='python', dtype=str, na_filter=True)
   df.loc[0, 'b']

Notice how we now instead output np.nan itself instead of a stringified form of it.

Plotting

Groupby/Resample/Rolling

Reshaping

Sparse

Build Changes

Other

Contributors

.. contributors:: v0.23.4..HEAD