add doc-string

Author: GYHHAHA

pandas/core/generic.py

@@ -7973,8 +7973,9 @@ def resample(
             `DatetimeIndex`, `TimedeltaIndex` or `PeriodIndex`.
         closed : {'right', 'left'}, default None
             Which side of bin interval is closed. The default is 'left'
-            for all frequency offsets except for 'M', 'A', 'Q', 'BM',
-            'BA', 'BQ', and 'W' which all have a default of 'right'.
+            for all frequency offsets with forward resampling except for 'M',
+            'A', 'Q', 'BM', 'BA', 'BQ', and 'W' which all have a default of
+            'right'. When `Backward` set to be True, default is 'right'.
         label : {'right', 'left'}, default None
             Which bin edge label to label bucket with. The default is 'left'
             for all frequency offsets except for 'M', 'A', 'Q', 'BM',
@@ -8007,7 +8008,7 @@ def resample(
         level : str or int, optional
             For a MultiIndex, level (name or number) to use for
             resampling. `level` must be datetime-like.
-        origin : {'epoch', 'start', 'start_day'}, Timestamp or str, default 'start_day'
+        origin : {'epoch', 'start', 'start_day', 'end', 'end_day'}, Timestamp or str, default 'start_day'
             The timestamp on which to adjust the grouping. The timezone of origin
             must match the timezone of the index.
             If a timestamp is not used, these values are also supported:
@@ -8018,6 +8019,21 @@ def resample(
 
             .. versionadded:: 1.1.0
 
+            - 'end': `origin` is the last value of the timeseries
+            - 'end_day': `origin` is the ceiling midnight of the last day
+
+            .. versionadded:: 1.2.0
+
+        backward : bool, default is None
+            Resample on the given `origin` from a backward direction. True when
+            `origin` is 'end' or 'end_day'. False when `origin` is 'start' or
+            'start_day'. Optional when using datetime `origin` , and default
+            False. The resample result for a specified datetime stands for the
+            group from time substract the given `freq` to time with a right
+            `closed` setting by default.
+
+            .. versionadded:: 1.2.0
+
         offset : Timedelta or str, default is None
             An offset timedelta added to the origin.
 
@@ -8297,6 +8313,28 @@ def resample(
         2000-10-02 00:21:00    24
         Freq: 17T, dtype: int64
 
+        If you want to take the last timestamp as `origin` with a backward resample:
+
+        >>> ts.index.max()
+        Timestamp('2000-10-02 00:26:00', freq='7T')
+        >>> ts.groupby(pd.Grouper(freq='17min', origin='end')).sum()
+        2000-10-01 23:35:00     0
+        2000-10-01 23:52:00    18
+        2000-10-02 00:09:00    27
+        2000-10-02 00:26:00    63
+        Freq: 17T, dtype: int32
+
+        You can also specify the backward origin:
+
+        >>> ts.groupby(pd.Grouper(freq='17min',
+                                  origin='2000-10-02 00:30:00',
+                                  backward=True)).sum()
+        2000-10-01 23:39:00     3
+        2000-10-01 23:56:00    15
+        2000-10-02 00:13:00    45
+        2000-10-02 00:30:00    45
+        Freq: 17T, dtype: int32
+
         To replace the use of the deprecated `base` argument, you can now use `offset`,
         in this example it is equivalent to have `base=2`:
 

pandas/core/groupby/grouper.py

@@ -83,9 +83,9 @@ class Grouper:
             However, loffset is also deprecated for ``.resample(...)``
             See: :class:`DataFrame.resample`
 
-    origin : {'epoch', 'start', 'start_day'}, Timestamp or str, default 'start_day'
-        The timestamp on which to adjust the grouping. The timezone of origin must
-        match the timezone of the index.
+    origin : {'epoch', 'start', 'start_day', 'end', 'end_day'}, Timestamp or str, default 'start_day'
+        The timestamp on which to adjust the grouping. The timezone of origin
+        must match the timezone of the index.
         If a timestamp is not used, these values are also supported:
 
         - 'epoch': `origin` is 1970-01-01
@@ -94,6 +94,21 @@ class Grouper:
 
         .. versionadded:: 1.1.0
 
+        - 'end': `origin` is the last value of the timeseries
+        - 'end_day': `origin` is the ceiling midnight of the last day
+
+        .. versionadded:: 1.2.0
+
+    backward : bool, default is None
+        Resample on the given `origin` from a backward direction. True when
+        `origin` is 'end' or 'end_day'. False when `origin` is 'start' or
+        'start_day'. Optional when using datetime `origin` , and default
+        False. The resample result for a specified datetime stands for the
+        group from time substract the given `freq` to time with a right
+        `closed` setting by default.
+
+        .. versionadded:: 1.2.0
+
     offset : Timedelta or str, default is None
         An offset timedelta added to the origin.
 
@@ -200,6 +215,15 @@ class Grouper:
     2000-10-02 00:15:00    45
     Freq: 17T, dtype: int64
 
+    If you want to take the last timestamp as `origin` with a backward resample:
+
+    >>> ts.groupby(pd.Grouper(freq='17min', origin='end')).sum()
+    2000-10-01 23:39:00    0
+    2000-10-01 23:56:00    0
+    2000-10-02 00:13:00    3
+    2000-10-02 00:30:00    6
+    Freq: 17T, dtype: int32
+
     If you want to adjust the start of the bins with an `offset` Timedelta, the two
     following lines are equivalent:
 

pandas/core/resample.py

@@ -1430,11 +1430,15 @@ def __init__(
                 self.backward = False
         elif backward:
             if origin in ("start", "start_day"):
-                raise ValueError(f"`start` or `start_day` origin isn't allowed when `backward` is True")
+                raise ValueError(
+                    f"`start` or `start_day` origin isn't allowed when `backward` is True"
+                )
             self.backward = backward
         else:
             if origin in ("end", "end_day"):
-                raise ValueError(f"`end` or `end_day` origin isn't allowed when `backward` is False")
+                raise ValueError(
+                    f"`end` or `end_day` origin isn't allowed when `backward` is False"
+                    )
             self.backward = backward
 
         try:
@@ -1785,7 +1789,13 @@ def _get_timestamp_range_edges(
                 origin = origin.tz_localize(None)
 
         first, last = _adjust_dates_anchored(
-            first, last, freq, closed=closed, origin=origin, backward=backward, offset=offset
+            first,
+            last,
+            freq,
+            closed=closed,
+            origin=origin,
+            backward=backward,
+            offset=offset,
         )
         if isinstance(freq, Day):
             first = first.tz_localize(index_tz)
@@ -1847,7 +1857,13 @@ def _get_period_range_edges(
     adjust_last = freq.is_on_offset(last)
 
     first, last = _get_timestamp_range_edges(
-        first, last, freq, closed=closed, origin=origin, backward=backward, offset=offset
+        first,
+        last,
+        freq,
+        closed=closed,
+        origin=origin,
+        backward=backward,
+        offset=offset,
     )
 
     first = (first + int(adjust_first) * freq).to_period(freq)
@@ -1873,7 +1889,7 @@ def _adjust_dates_anchored(
             if origin == "end":
                 origin = last
             elif origin == "end_day":
-                origin = last.ceil('D')
+                origin = last.ceil("D")
             sub_freq_times = (origin.value - first.value) // freq.nanos
             if closed == "left":
                 sub_freq_times += 1