151 lines
4.7 KiB
Markdown
151 lines
4.7 KiB
Markdown
# nested_iters
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{:.no_toc}
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<nav markdown="1" class="toc-class">
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* TOC
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{:toc}
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</nav>
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## Top
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Questions to [David Rotermund](mailto:davrot@uni-bremen.de)
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{: .topic-optional}
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This is an optional topic!
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## [numpy.nested_iters](https://numpy.org/doc/stable/reference/generated/numpy.nested_iters.html)
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```python
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numpy.nested_iters(op, axes, flags=None, op_flags=None, op_dtypes=None, order='K', casting='safe', buffersize=0)
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```
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> Create nditers for use in nested loops
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>
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> Create a tuple of nditer objects which iterate in nested loops over different axes of the op argument. The first iterator is used in the outermost loop, the last in the innermost loop. Advancing one will change the subsequent iterators to point at its new element.
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### 2d
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```python
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import numpy as np
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a = np.arange(1, 7).reshape((2, 3))
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print(a)
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print()
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iter_a, iter_b = np.nested_iters(a, [[0], [1]], flags=["multi_index"])
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for x in iter_a:
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for y in iter_b:
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print(
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f"iter_a.multi_index: {iter_a.multi_index}, iter_b.multi_index: {iter_b.multi_index}"
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)
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```
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Output:
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```python
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[[1 2 3]
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[4 5 6]]
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iter_a.multi_index: (0,), iter_b.multi_index: (0,)
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iter_a.multi_index: (0,), iter_b.multi_index: (1,)
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iter_a.multi_index: (0,), iter_b.multi_index: (2,)
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iter_a.multi_index: (1,), iter_b.multi_index: (0,)
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iter_a.multi_index: (1,), iter_b.multi_index: (1,)
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iter_a.multi_index: (1,), iter_b.multi_index: (2,)
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```
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### 3d
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```python
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import numpy as np
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a = np.zeros((2, 3, 4))
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print(a.shape) # -> (2, 3, 4)
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print("------")
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iter_a, iter_b = np.nested_iters(a, [[0], [1, 2]], flags=["multi_index"])
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for x in iter_a:
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for y in iter_b:
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print(
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f"iter_a.multi_index: {iter_a.multi_index}, iter_b.multi_index: {iter_b.multi_index}"
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)
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print("------")
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print("++++++")
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iter_a, iter_b = np.nested_iters(a, [[0, 1], [2]], flags=["multi_index"])
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for x in iter_a:
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for y in iter_b:
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print(
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f"iter_a.multi_index: {iter_a.multi_index}, iter_b.multi_index: {iter_b.multi_index}"
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)
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print("++++++")
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```
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Output:
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```python
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------
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iter_a.multi_index: (0,), iter_b.multi_index: (0, 0)
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iter_a.multi_index: (0,), iter_b.multi_index: (0, 1)
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iter_a.multi_index: (0,), iter_b.multi_index: (0, 2)
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iter_a.multi_index: (0,), iter_b.multi_index: (0, 3)
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iter_a.multi_index: (0,), iter_b.multi_index: (1, 0)
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iter_a.multi_index: (0,), iter_b.multi_index: (1, 1)
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iter_a.multi_index: (0,), iter_b.multi_index: (1, 2)
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iter_a.multi_index: (0,), iter_b.multi_index: (1, 3)
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iter_a.multi_index: (0,), iter_b.multi_index: (2, 0)
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iter_a.multi_index: (0,), iter_b.multi_index: (2, 1)
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iter_a.multi_index: (0,), iter_b.multi_index: (2, 2)
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iter_a.multi_index: (0,), iter_b.multi_index: (2, 3)
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iter_a.multi_index: (1,), iter_b.multi_index: (0, 0)
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iter_a.multi_index: (1,), iter_b.multi_index: (0, 1)
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iter_a.multi_index: (1,), iter_b.multi_index: (0, 2)
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iter_a.multi_index: (1,), iter_b.multi_index: (0, 3)
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iter_a.multi_index: (1,), iter_b.multi_index: (1, 0)
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iter_a.multi_index: (1,), iter_b.multi_index: (1, 1)
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iter_a.multi_index: (1,), iter_b.multi_index: (1, 2)
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iter_a.multi_index: (1,), iter_b.multi_index: (1, 3)
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iter_a.multi_index: (1,), iter_b.multi_index: (2, 0)
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iter_a.multi_index: (1,), iter_b.multi_index: (2, 1)
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iter_a.multi_index: (1,), iter_b.multi_index: (2, 2)
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iter_a.multi_index: (1,), iter_b.multi_index: (2, 3)
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------
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++++++
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iter_a.multi_index: (0, 0), iter_b.multi_index: (0,)
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iter_a.multi_index: (0, 0), iter_b.multi_index: (1,)
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iter_a.multi_index: (0, 0), iter_b.multi_index: (2,)
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iter_a.multi_index: (0, 0), iter_b.multi_index: (3,)
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iter_a.multi_index: (0, 1), iter_b.multi_index: (0,)
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iter_a.multi_index: (0, 1), iter_b.multi_index: (1,)
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iter_a.multi_index: (0, 1), iter_b.multi_index: (2,)
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iter_a.multi_index: (0, 1), iter_b.multi_index: (3,)
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iter_a.multi_index: (0, 2), iter_b.multi_index: (0,)
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iter_a.multi_index: (0, 2), iter_b.multi_index: (1,)
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iter_a.multi_index: (0, 2), iter_b.multi_index: (2,)
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iter_a.multi_index: (0, 2), iter_b.multi_index: (3,)
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iter_a.multi_index: (1, 0), iter_b.multi_index: (0,)
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iter_a.multi_index: (1, 0), iter_b.multi_index: (1,)
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iter_a.multi_index: (1, 0), iter_b.multi_index: (2,)
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iter_a.multi_index: (1, 0), iter_b.multi_index: (3,)
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iter_a.multi_index: (1, 1), iter_b.multi_index: (0,)
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iter_a.multi_index: (1, 1), iter_b.multi_index: (1,)
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iter_a.multi_index: (1, 1), iter_b.multi_index: (2,)
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iter_a.multi_index: (1, 1), iter_b.multi_index: (3,)
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iter_a.multi_index: (1, 2), iter_b.multi_index: (0,)
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iter_a.multi_index: (1, 2), iter_b.multi_index: (1,)
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iter_a.multi_index: (1, 2), iter_b.multi_index: (2,)
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iter_a.multi_index: (1, 2), iter_b.multi_index: (3,)
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++++++
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```
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For higher dimensions, we can partition the indices into groups (if we want to). e.g. 4 dims:
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[[0,1], [2,3]] or [[0],[1],[2],[3]] or [[0,1,2],[3]],...
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