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Consolidate offset string handling into factory _from_str #9709

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Consolidate offset string handling into factory _from_str #9709

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107c08a
consolidate freqstr handling
isVoid Nov 16, 2021
25da96e
.
isVoid Nov 16, 2021
cbbc061
reject ambiguous input and add raise error message for unsupported ty…
isVoid Nov 18, 2021
0208eaf
Apply suggestions from code review
isVoid Nov 24, 2021
b3491e8
do not explicitly test for unsupported types
isVoid Nov 24, 2021
561caca
Merge branch 'improvements/offset_str_handling' of github.com:isVoid/…
isVoid Nov 24, 2021
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52 changes: 23 additions & 29 deletions python/cudf/cudf/core/tools/datetimes.py
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Original file line number Diff line number Diff line change
Expand Up @@ -38,6 +38,8 @@
"min": "m",
"s": "s",
"S": "s",
"L": "ms",
"ms": "ms",
"U": "us",
"us": "us",
"N": "ns",
Expand Down Expand Up @@ -448,7 +450,6 @@ class DateOffset:
"ns": "nanoseconds",
"us": "microseconds",
"ms": "milliseconds",
"L": "milliseconds",
"s": "seconds",
"m": "minutes",
"h": "hours",
Expand All @@ -458,7 +459,7 @@ class DateOffset:
"Y": "years",
}

_FREQSTR_REGEX = re.compile("([0-9]*)([a-zA-Z]+)")
_FREQSTR_REGEX = re.compile("(-)*([0-9]*)([a-zA-Z]+)")
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It looks like this might be the regex pandas uses, which handles a lot of cases this regex may miss. (This regex might not be for exactly the same purpose, but it demonstrates the types of cases we might need to handle.)

r"([+\-]?\d*|[+\-]?\d*\.\d*)\s*([A-Za-z]+([\-][\dA-Za-z\-]+)?)"
https://github.com/pandas-dev/pandas/blob/8fefaa5a9a7c3f3a1c35c36c1140117dab73c9c7/pandas/_libs/tslibs/offsets.pyx#L3506-L3508

Do we need to support frequencies like +10ms? What about spaces in between like 3 h? I'd check these cases against pandas to see what is supported -- or find the exact regex that pandas uses to make sure we hit the same cases.

Suggested change
_FREQSTR_REGEX = re.compile("(-)*([0-9]*)([a-zA-Z]+)")
_FREQSTR_REGEX = re.compile("([+\-])?(\d*)\s*([A-Za-z]+)")


def __init__(self, n=1, normalize=False, **kwds):
if normalize:
Expand Down Expand Up @@ -629,27 +630,32 @@ def __repr__(self):
return repr_str

@classmethod
def _from_freqstr(cls: Type[_T], freqstr: str) -> _T:
def _from_str(cls: Type[_T], freqstr: str) -> _T:
"""
Parse a string and return a DateOffset object
expects strings of the form 3D, 25W, 10ms, 42ns, etc.
"""
match = cls._FREQSTR_REGEX.match(freqstr)
Parse a string and return a DateOffset object.

Expects strings of the form 3D, 25W, 10ms, 42ns, etc.
See `_offset_alias_to_code` and `_CODE_TO_UNITS` for
supported list of strings.
"""
match = cls._FREQSTR_REGEX.fullmatch(freqstr)
if match is None:
raise ValueError(f"Invalid frequency string: {freqstr}")

numeric_part = match.group(1)
if numeric_part == "":
numeric_part = "1"
freq_part = match.group(2)

if freq_part not in cls._CODES_TO_UNITS:
sign_part, numeric_part, freq_part = match.groups()
if freq_part in _offset_alias_to_code:
code = _offset_alias_to_code[freq_part]
elif freq_part in cls._CODES_TO_UNITS:
code = freq_part
else:
raise ValueError(f"Cannot interpret frequency str: {freqstr}")

return cls(**{cls._CODES_TO_UNITS[freq_part]: int(numeric_part)})
sign = -1 if sign_part else 1
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Needed for my other regex suggestion above.

Suggested change
sign = -1 if sign_part else 1
sign = -1 if sign_part.startswith("-") else 1

n = int(numeric_part) if numeric_part else 1

def _maybe_as_fast_pandas_offset(self):
return cls(**{cls._CODES_TO_UNITS[code]: n * sign})

def _maybe_as_fast_pandas_offset(self) -> pd.DateOffset:
if (
len(self.kwds) == 1
and _has_fixed_frequency(self)
Expand Down Expand Up @@ -814,23 +820,11 @@ def date_range(
if isinstance(freq, DateOffset):
offset = freq
elif isinstance(freq, str):
# Map pandas `offset alias` into cudf DateOffset `CODE`, only
# fixed-frequency, non-anchored offset aliases are supported.
mo = re.fullmatch(
rf'(-)*(\d*)({"|".join(_offset_alias_to_code.keys())})', freq
)
if mo is None:
offset = DateOffset._from_str(freq)
if "months" in offset.kwds or "years" in offset.kwds:
raise ValueError(
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f"Unrecognized or unsupported offset alias {freq}."
)

sign, n, offset_alias = mo.groups()
code = _offset_alias_to_code[offset_alias]

freq = "".join([n, code])
offset = DateOffset._from_freqstr(freq)
if sign:
offset.kwds.update({s: -i for s, i in offset.kwds.items()})
else:
raise TypeError("`freq` must be a `str` or cudf.DateOffset object.")

Expand Down