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manipulating non-missing elements in a field

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4/5
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3-5 天
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35/100
Issue 类型
功能
描述清晰度
基本清楚
活跃度
停滞
技术栈
numpy, python, scikit-learn
领域
data

调研方向

首先检查报告中提到的 CF 字段和 Data 入口点:compressed()、reshape()、get_data() 和 set_data(),包括掩码数组和由 dask 支持的数组是如何处理的。定义用于提取非缺失值和赋值结果的便利操作,然后为 3D-to-2D 工作流以及 dask chunk 大小未知的情况添加覆盖。

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描述

dask enhancement question

In order to use a scikit regression module, I need to

  • Extract the non-missing elements from a 3D field fin(z,y,x) into a numpy array (z,p), where p is a 1D index over all the non-missing (y,x) locations, which are the same for every z.

  • Put a 1D array of results r(p) into the non-missing data elements of a 2D field fout(y,x).

I've done it as follows:

findata=fin.data.compressed().to_dask_array()
findata.compute_chunk_sizes()
findata=findata.reshape(fin.shape[0],fin[0,:].data.compressed().size)
# compute r from findata
foutdata=fout.get_data().flatten()
foutdata[~foutdata.mask]=r
fout.set_data(foutdata.reshape(fout.shape))

Are there better ways, or could you provide better ways? The following occur to me:

  • It would be handy if compressed() was a method of a CF field, to flatten it into a 1D array containing only the non-missing values.
  • I needed three lines to produce findata because of having to compute_chunk_sizes on the dask array. Without that step, I got errors as below.
  • Is there a way to avoid having to get the Data out of the field in order to assign to some elements of it using the mask? This was a bit clumsy.

In the Met O IDL lib, both input and output are easier:

findata=fin.data(where(fin(0).data ne fin(0).bmdi))
; compute r from findata
fout.data(where(fout.data ne fout.bmdi))=r

It would be good to have something equally convenient in cf-python. Perhaps there is?

Here's the dask problem:

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/home/users/sws02jmg/.local/lib/python3.11/site-packages/cfdm/decorators.py", line 44, in inplace_wrapper
    processed_copy = operation_method(self, *args, **kwargs)
                     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/users/sws02jmg/.local/lib/python3.11/site-packages/cf/data/data.py", line 10489, in reshape
    dx = dx.reshape(*shape, merge_chunks=merge_chunks, limit=limit)
         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/software/applications/anaconda/2023.09-0/lib/python3.11/site-packages/dask/array/core.py", line 2220, in reshape
    return reshape(self, shape, merge_chunks=merge_chunks, limit=limit)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/software/applications/anaconda/2023.09-0/lib/python3.11/site-packages/dask/array/reshape.py", line 222, in reshape
    raise ValueError(
ValueError: Array chunk size or shape is unknown. shape: (nan,)

Possible solution with x.compute_chunk_sizes()

Thanks. Jonathan

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