other:python:misc_by_jyp
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other:python:misc_by_jyp [2022/03/08 16:40] jypeter [Playing with strings] |
other:python:misc_by_jyp [2022/05/23 16:01] jypeter [numpy related stuff] Changed the VIEW update warnng example |
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| ==== numpy related stuff ==== | ==== numpy related stuff ==== | ||
| + | |||
| + | === Dealing with a variable number of indices === | ||
| + | |||
| + | [[https://numpy.org/doc/stable/user/basics.indexing.html#dealing-with-variable-indices|Official reference]] | ||
| + | |||
| + | <code>>>> i10 = np.identity(10) | ||
| + | >>> i10 | ||
| + | array([[1., 0., 0., 0., 0., 0., 0., 0., 0., 0.], | ||
| + | [0., 1., 0., 0., 0., 0., 0., 0., 0., 0.], | ||
| + | ... | ||
| + | [0., 0., 0., 0., 0., 0., 0., 0., 0., 1.]]) | ||
| + | >>> i10.shape | ||
| + | (10, 10) | ||
| + | |||
| + | >>> i10[3:7, 4:6] | ||
| + | array([[0., 0.], | ||
| + | [1., 0.], | ||
| + | [0., 1.], | ||
| + | [0., 0.]]) | ||
| + | |||
| + | >>> s0 = slice(3, 7) | ||
| + | >>> s1 = slice(4, 6) | ||
| + | >>> i10[s0, s1] | ||
| + | array([[0., 0.], | ||
| + | [1., 0.], | ||
| + | [0., 1.], | ||
| + | [0., 0.]]) | ||
| + | |||
| + | >>> my_slices = (s0, s1) | ||
| + | >>> i10[my_slices] | ||
| + | array([[0., 0.], | ||
| + | [1., 0.], | ||
| + | [0., 1.], | ||
| + | [0., 0.]]) | ||
| + | |||
| + | >>> my_fancy_slices = (s0, Ellipsis) | ||
| + | >>> i10[my_fancy_slices] | ||
| + | array([[0., 0., 0., 1., 0., 0., 0., 0., 0., 0.], | ||
| + | [0., 0., 0., 0., 1., 0., 0., 0., 0., 0.], | ||
| + | [0., 0., 0., 0., 0., 1., 0., 0., 0., 0.], | ||
| + | [0., 0., 0., 0., 0., 0., 1., 0., 0., 0.]]) | ||
| + | >>> i10[my_fancy_slices].shape | ||
| + | (4, 10) | ||
| + | |||
| + | >>> # WARNING! DANGERRRR! NEVER forget that a VIEW is NOT A COPY | ||
| + | >>> # and that you can change the content of the original array by mistake | ||
| + | >>> my_view = i10[my_slices] | ||
| + | >>> my_view[:, :] = -1 | ||
| + | >>> my_view | ||
| + | array([[-1., -1.], | ||
| + | [-1., -1.], | ||
| + | [-1., -1.], | ||
| + | [-1., -1.]]) | ||
| + | >>> i10 | ||
| + | array([[ 1., 0., 0., 0., 0., 0., 0., 0., 0., 0.], | ||
| + | [ 0., 1., 0., 0., 0., 0., 0., 0., 0., 0.], | ||
| + | [ 0., 0., 1., 0., 0., 0., 0., 0., 0., 0.], | ||
| + | [ 0., 0., 0., 1., -1., -1., 0., 0., 0., 0.], | ||
| + | [ 0., 0., 0., 0., -1., -1., 0., 0., 0., 0.], | ||
| + | [ 0., 0., 0., 0., -1., -1., 0., 0., 0., 0.], | ||
| + | [ 0., 0., 0., 0., -1., -1., 1., 0., 0., 0.], | ||
| + | [ 0., 0., 0., 0., 0., 0., 0., 1., 0., 0.], | ||
| + | [ 0., 0., 0., 0., 0., 0., 0., 0., 1., 0.], | ||
| + | [ 0., 0., 0., 0., 0., 0., 0., 0., 0., 1.]])</code> | ||
| === Finding and counting unique values === | === Finding and counting unique values === | ||
other/python/misc_by_jyp.txt · Last modified: 2024/04/19 12:02 by jypeter
