ENH: Added stride/offset aliases in to_datetime

pandas/_libs/tslibs/timedeltas.pyx

@@ -26,6 +26,8 @@ from pandas._libs.tslibs.c_timestamp cimport _Timestamp
 
 from pandas._libs.tslibs.ccalendar import DAY_SECONDS
 
+from pandas._libs.tslibs.frequencies import _base_and_stride
+
 from pandas._libs.tslibs.np_datetime cimport (
     cmp_scalar, reverse_ops, td64_to_tdstruct, pandas_timedeltastruct)
 
@@ -252,35 +254,54 @@ cpdef inline object precision_from_unit(object unit):
         int64_t m
         int p
 
-    if unit == 'Y':
-        m = 1000000000L * 31556952
+    if unit is None:
+        m = 1L
+        p = 0
+        return m, p
+
+    unit, stride = _base_and_stride(unit)
+
+    # Normalize old or lowercase codes to standard offset aliases.
+    if unit in ['min', 'm']:
+        unit = 'T'
+    elif unit == 'ns':
+        unit = 'N'
+    elif unit == 'ms':
+        unit = 'L'
+    elif unit == 'us':
+        unit = 'U'
+
+    unit = unit.upper()
+
+    if unit in ['Y', 'A']:
+        m = stride * 1000000000L * 31556952
         p = 9
     elif unit == 'M':
-        m = 1000000000L * 2629746
+        m = stride * 1000000000L * 2629746
         p = 9
     elif unit == 'W':
-        m = 1000000000L * DAY_SECONDS * 7
+        m = stride * 1000000000L * DAY_SECONDS * 7
         p = 9
-    elif unit == 'D' or unit == 'd':
-        m = 1000000000L * DAY_SECONDS
+    elif unit == 'D':
+        m = stride * 1000000000L * DAY_SECONDS
         p = 9
-    elif unit == 'h':
-        m = 1000000000L * 3600
+    elif unit == 'H':
+        m = stride * 1000000000L * 3600
         p = 9
-    elif unit == 'm':
-        m = 1000000000L * 60
+    elif unit == 'T':
+        m = stride * 1000000000L * 60
         p = 9
-    elif unit == 's':
-        m = 1000000000L
+    elif unit == 'S':
+        m = stride * 1000000000L
         p = 9
-    elif unit == 'ms':
-        m = 1000000L
+    elif unit == 'L':
+        m = stride * 1000000L
         p = 6
-    elif unit == 'us':
-        m = 1000L
+    elif unit == 'U':
+        m = stride * 1000L
         p = 3
-    elif unit == 'ns' or unit is None:
-        m = 1L
+    elif unit == 'N':
+        m = stride * 1L
         p = 0
     else:
         raise ValueError("cannot cast unit {unit}".format(unit=unit))
@@ -300,7 +321,7 @@ cdef inline int64_t cast_from_unit(object ts, object unit) except? -1:
     if ts is None:
         return m
 
-    # cast the unit, multiply base/frace separately
+    # cast the unit, multiply base/frac separately
     # to avoid precision issues from float -> int
     base = <int64_t>ts
     frac = ts - base

pandas/core/tools/datetimes.py

@@ -470,11 +470,26 @@ def to_datetime(arg, errors='raise', dayfirst=False, yearfirst=False,
         - If True, require an exact format match.
         - If False, allow the format to match anywhere in the target string.
 
-    unit : string, default 'ns'
-        unit of the arg (D,s,ms,us,ns) denote the unit, which is an
-        integer or float number. This will be based off the origin.
-        Example, with unit='ms' and origin='unix' (the default), this
-        would calculate the number of milliseconds to the unix epoch start.
+    unit : string, default is 'N'
+        The unit of the arg. Uses a subset of the pandas offset aliases.
+
+        - 'Y', 'A' for yearly (long term average of 365.2425 days)
+        - 'M' for monthly (long term average of 30.436875 days)
+        - 'W' for weekly
+        - 'D' for daily
+        - 'H' for hourly
+        - 'T', 'min' for minutely
+        - 'S' for seconds
+        - 'L', 'ms' for milliseconds
+        - 'U', 'us' for microseconds
+        - 'N' for nanoseconds
+
+        This will be based off the origin.  Example, with unit='L' and
+        origin='unix' (the default), this would calculate the number of
+        milliseconds to the unix epoch start.
+
+        The offset alias can be prefixed with a stride. For example, results
+        would be equivalent between unit='7D' and unit='W'.
     infer_datetime_format : boolean, default False
         If True and no `format` is given, attempt to infer the format of the
         datetime strings, and if it can be inferred, switch to a faster