93 lines
1.7 KiB
Markdown
93 lines
1.7 KiB
Markdown
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# Concatenate
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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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## The goal
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Questions to [David Rotermund](mailto:davrot@uni-bremen.de)
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## [numpy.concatenate]()
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```python
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numpy.concatenate((a1, a2, ...), axis=0, out=None, dtype=None, casting="same_kind")
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```
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> Join a sequence of arrays along an existing axis.
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```python
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import numpy as np
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a = np.arange(0, 5)
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print(a) # -> [0 1 2 3 4]
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print(a.shape) # -> (5,)
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b = np.arange(0, 8)
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print(b) # -> [0 1 2 3 4 5 6 7]
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print(b.shape) # -> (8,)
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c = np.concatenate((a, b))
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print(c) # -> [0 1 2 3 4 0 1 2 3 4 5 6 7]
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print(c.shape) # -> (13,)
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print(np.may_share_memory(a, c)) # -> False (Copy)
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c = np.concatenate((a, b), axis=0)
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print(c) # -> [0 1 2 3 4 0 1 2 3 4 5 6 7]
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print(c.shape) # -> (13,)
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print(np.may_share_memory(a, c)) # -> False (Copy)
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c = np.concatenate(
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(a, b), axis=1
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) # AxisError: axis 1 is out of bounds for array of dimension 1
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```
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concatenate does not add necessary dimensions, you have to do that yourself:
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```python
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import numpy as np
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a = np.arange(0, 10)
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print(a.shape) # -> (10,)
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b = np.arange(0, 10)
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print(b.shape) # -> (10,)
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c = np.concatenate((a, b), axis=0)
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print(c.shape) # -> (20,)
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c = np.concatenate((a, b), axis=1) # AxisError: axis 1 is out of bounds for array of dimension 1
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```
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```python
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import numpy as np
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a = np.arange(0, 10)[:, np.newaxis]
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print(a.shape) # -> (10,1)
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b = np.arange(0, 10)[:, np.newaxis]
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print(b.shape) # -> (10,1)
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c = np.concatenate((a, b), axis=0)
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print(c.shape) # -> (20,1)
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c = np.concatenate((a, b), axis=1)
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print(c)
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print(c.shape) # -> (10,2)
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```
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```python
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[[0 0]
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[1 1]
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[2 2]
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[3 3]
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[4 4]
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[5 5]
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[6 6]
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[7 7]
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[8 8]
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[9 9]]
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```
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