将项目分配给Python dask数组对象

问题描述：

我创建了一个Python dask数组，并尝试按如下所示修改数组的一部分：

I've created a Python dask array and I'm trying to modify a slice of the array as follows:

import numpy as np
import dask.array as da

x = np.random.random((20000, 100, 100)) # Create numpy array
dx = da.from_array(x, chunks=(x.shape[0], 10, 10)) # Create dask array from numpy array

dx[:50, :, :] = 0 # Modify a slice of the dask array

尝试修改dask数组会引发异常：

Such an attempt to modify the dask array raises the exception:

TypeError: 'Array' object does not support item assignment

是否可以在不引发异常的情况下修改dask数组切片？

Is there a way to modify a dask array slice without raising an exception?

答

当前 dask.array 不支持项目分配或任何其他突变操作。

Currently dask.array does not support item assignment or any other mutation operation.

在上述情况下，我建议使用零连接

In the case above I recommend concatenating with zeros

In [1]: import dask.array as da

In [2]: dx = da.random.random((20000 - 50, 100, 100), chunks=(None, 10, 10))

In [3]: z = da.zeros((50, 100, 100), chunks=(50, 10, 10))

In [4]: dx2 = da.concatenate([z, dx], axis=0)

In [5]: dx2
Out[5]: dask.array<concate..., shape=(20000, 100, 100), dtype=float64, chunksize=(50, 10, 10)>

In [6]: (dx2 == 0)[0:100, 0, 0].compute()
Out[6]: 
array([ True,  True,  True,  True,  True,  True,  True,  True,  True,
        True,  True,  True,  True,  True,  True,  True,  True,  True,
        True,  True,  True,  True,  True,  True,  True,  True,  True,
        True,  True,  True,  True,  True,  True,  True,  True,  True,
        True,  True,  True,  True,  True,  True,  True,  True,  True,
        True,  True,  True,  True,  True, False, False, False, False,
       False, False, False, False, False, False, False, False, False,
       False, False, False, False, False, False, False, False, False,
       False, False, False, False, False, False, False, False, False,
       False, False, False, False, False, False, False, False, False,
       False, False, False, False, False, False, False, False, False, False], dtype=bool)

da.where（条件，iftrue，iffalse）函数在解决经常需要突变的情况下也非常有用。

The da.where(condition, iftrue, iffalse) function can also be quite useful in working around cases where mutation is often desired.

将项目分配给Python dask数组对象

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