Dask array mean抛出“setting an array element with a sequence”异常,其中pandas array mean起作用

我有一个由一列numpy数组组成的pandas数据帧。我可以使用 numpy.mean

import numpy
import pandas
f = pandas.DataFrame({"a":[numpy.array([1.0, 2.0]), numpy.array([3.0, 4.0])]})
numpy.mean(f["a"]) # returns array([2., 3.])

我也想在达斯克做同样的事。

import dask.dataframe
import dask.array
g = dask.dataframe.from_pandas(f, npartitions=1)
dask.array.mean(g["a"], dtype="float64")

(您必须指定 dtype ,否则你会得到 TypeError: unsupported operand type(s) for /: 'NoneType' and 'int' 例外情况。)

dask.array.mean 返回以下看起来正确的值。

dask.array<mean_agg-aggregate, shape=(), dtype=float64, chunksize=(), chunktype=numpy.ndarray>

但是,当我跑的时候 dask.array.mean(g["a"], dtype="float64").compute() 为了得到最终值,我得到一个 ValueError: setting an array element with a sequence. 例外。完整堆栈如下所示。

Traceback (most recent call last):
  File "/Applications/PyCharm.app/Contents/plugins/python/helpers/pydev/_pydevd_bundle/pydevd_exec2.py", line 3, in Exec
    exec(exp, global_vars, local_vars)
  File "<input>", line 1, in <module>
  File "/Users/wmcneill/src.private/radius_limit/venv/lib/python3.7/site-packages/dask/base.py", line 165, in compute
    (result,) = compute(self, traverse=False, **kwargs)
  File "/Users/wmcneill/src.private/radius_limit/venv/lib/python3.7/site-packages/dask/base.py", line 436, in compute
    results = schedule(dsk, keys, **kwargs)
  File "/Users/wmcneill/src.private/radius_limit/venv/lib/python3.7/site-packages/dask/threaded.py", line 81, in get
    **kwargs
  File "/Users/wmcneill/src.private/radius_limit/venv/lib/python3.7/site-packages/dask/local.py", line 486, in get_async
    raise_exception(exc, tb)
  File "/Users/wmcneill/src.private/radius_limit/venv/lib/python3.7/site-packages/dask/local.py", line 316, in reraise
    raise exc
  File "/Users/wmcneill/src.private/radius_limit/venv/lib/python3.7/site-packages/dask/local.py", line 222, in execute_task
    result = _execute_task(task, data)
  File "/Users/wmcneill/src.private/radius_limit/venv/lib/python3.7/site-packages/dask/core.py", line 118, in _execute_task
    args2 = [_execute_task(a, cache) for a in args]
  File "/Users/wmcneill/src.private/radius_limit/venv/lib/python3.7/site-packages/dask/core.py", line 118, in <listcomp>
    args2 = [_execute_task(a, cache) for a in args]
  File "/Users/wmcneill/src.private/radius_limit/venv/lib/python3.7/site-packages/dask/core.py", line 119, in _execute_task
    return func(*args2)
  File "/Users/wmcneill/src.private/radius_limit/venv/lib/python3.7/site-packages/dask/optimization.py", line 982, in __call__
    return core.get(self.dsk, self.outkey, dict(zip(self.inkeys, args)))
  File "/Users/wmcneill/src.private/radius_limit/venv/lib/python3.7/site-packages/dask/core.py", line 149, in get
    result = _execute_task(task, cache)
  File "/Users/wmcneill/src.private/radius_limit/venv/lib/python3.7/site-packages/dask/core.py", line 119, in _execute_task
    return func(*args2)
  File "/Users/wmcneill/src.private/radius_limit/venv/lib/python3.7/site-packages/dask/utils.py", line 29, in apply
    return func(*args, **kwargs)
  File "/Users/wmcneill/src.private/radius_limit/venv/lib/python3.7/site-packages/dask/array/reductions.py", line 539, in mean_chunk
    total = sum(x, dtype=dtype, **kwargs)
  File "<__array_function__ internals>", line 6, in sum
  File "/Users/wmcneill/src.private/radius_limit/venv/lib/python3.7/site-packages/numpy/core/fromnumeric.py", line 2229, in sum
    initial=initial, where=where)
  File "/Users/wmcneill/src.private/radius_limit/venv/lib/python3.7/site-packages/numpy/core/fromnumeric.py", line 90, in _wrapreduction
    return ufunc.reduce(obj, axis, dtype, out, **passkwargs)
ValueError: setting an array element with a sequence.

是否可以执行等效的Dask操作?