将项目分配给Python dask数组对象 [英] Item assignment to Python dask array objects
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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?
推荐答案
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.
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