如何将pyarrow时间戳数据类型转换为time64类型？

Question

我正在尝试将pyarrow时间戳类型转换为time64类型。但它显示了演员错误

import pyarrow as pa
from datetime import datetime

dt = datetime.now()
table = pa.Table.from_pydict({'ts': pa.array([dt, dt])})
new_schema = table.schema.set(0, pa.field('ts', pa.time64('us')))
table.schema
# ts: timestamp[us]
new_schema
# ts: time64[us]

table.cast(new_schema)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "pyarrow/table.pxi", line 1329, in pyarrow.lib.Table.cast
  File "pyarrow/table.pxi", line 277, in pyarrow.lib.ChunkedArray.cast
  File "/home/inspiron/.virtualenvs/par/lib/python3.7/site-packages/pyarrow/compute.py", line 243, in cast
    return call_function("cast", [arr], options)
  File "pyarrow/_compute.pyx", line 446, in pyarrow._compute.call_function
  File "pyarrow/_compute.pyx", line 275, in pyarrow._compute.Function.call
  File "pyarrow/error.pxi", line 122, in pyarrow.lib.pyarrow_internal_check_status
  File "pyarrow/error.pxi", line 105, in pyarrow.lib.check_status
pyarrow.lib.ArrowNotImplementedError: Unsupported cast from timestamp[us] to time64 using function cast_time64

有什么方法可以让这个角色成为可能吗

Answer 1

time64[us]是一天中的一段时间。它表示自午夜以来的微秒数。它不绑定到任何特定日期，并且不能转换为时间戳

箭头文档有点稀疏，但是parquet docs解释得更好：

TIME

TIME is used for a logical time type without a date with millisecond or microsecond precision. The type has two type parameters: UTC adjustment (true or false) and unit (MILLIS or MICROS, NANOS).

TIME with unit MILLIS is used for millisecond precision. It must annotate an int32 that stores the number of milliseconds after midnight.

TIME with unit MICROS is used for microsecond precision. It must annotate an int64 that stores the number of microseconds after midnight.

TIME with unit NANOS is used for nanosecond precision. It must annotate an int64 that stores the number of nanoseconds after midnight.

The sort order used for TIME is signed.