other:python:misc_by_jyp
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other:python:misc_by_jyp [2022/05/23 15:36] jypeter [numpy related stuff] Added the "variable number of indices" section |
other:python:misc_by_jyp [2022/07/08 14:00] jypeter [numpy related stuff] Added the arbitrary object array |
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| ==== numpy related stuff ==== | ==== numpy related stuff ==== | ||
| + | === Using a numpy array to store arbitrary objects === | ||
| + | |||
| + | The numpy arrays are usually used to store [[https://numpy.org/doc/stable/reference/arrays.scalars.html|scalars]] of the same type (see also the [[https://numpy.org/doc/stable/reference/arrays.dtypes.html|Data type objects (dtype)]]), very often numerical values. | ||
| + | |||
| + | It is also possible to store **arbitrary** Python objects in an array, rather than using nested lists or dictionaries! | ||
| + | |||
| + | <code>>>> some_array = np.empty((2, 3), dtype=object) | ||
| + | >>> some_array | ||
| + | array([[None, None, None], | ||
| + | [None, None, None]], dtype=object) | ||
| + | >>> some_array.shape | ||
| + | (2, 3) | ||
| + | >>> print(some_array[-1, -1]) | ||
| + | None | ||
| + | >>> some_array[-1, 0] = filled_contour # e.g. save an existing cartopy filled contour object | ||
| + | >>> some_array | ||
| + | array([[None, None, None], | ||
| + | [<cartopy.mpl.contour.GeoContourSet object at 0x2ab679e8bf10>, | ||
| + | None, None]], dtype=object)</code> | ||
| + | | ||
| === Dealing with a variable number of indices === | === Dealing with a variable number of indices === | ||
| Line 291: | Line 311: | ||
| (4, 10) | (4, 10) | ||
| - | >>> # WARNING! WARNING! A slice is a VIEW and NOT A COPY | + | >>> # WARNING! DANGERRRR! NEVER forget that a VIEW is NOT A COPY |
| - | >>> i10[my_fancy_slices] = -1 | + | >>> # 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 | >>> i10 | ||
| array([[ 1., 0., 0., 0., 0., 0., 0., 0., 0., 0.], | array([[ 1., 0., 0., 0., 0., 0., 0., 0., 0., 0.], | ||
| [ 0., 1., 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., 1., 0., 0., 0., 0., 0., 0., 0.], | ||
| - | [-1., -1., -1., -1., -1., -1., -1., -1., -1., -1.], | + | [ 0., 0., 0., 1., -1., -1., 0., 0., 0., 0.], |
| - | [-1., -1., -1., -1., -1., -1., -1., -1., -1., -1.], | + | [ 0., 0., 0., 0., -1., -1., 0., 0., 0., 0.], |
| - | [-1., -1., -1., -1., -1., -1., -1., -1., -1., -1.], | + | [ 0., 0., 0., 0., -1., -1., 0., 0., 0., 0.], |
| - | [-1., -1., -1., -1., -1., -1., -1., -1., -1., -1.], | + | [ 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., 1., 0., 0.], | ||
| [ 0., 0., 0., 0., 0., 0., 0., 0., 1., 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., 1.]])</code> |
| - | </code> | + | |
| === Finding and counting unique values === | === Finding and counting unique values === | ||
other/python/misc_by_jyp.txt · Last modified: 2022/07/08 14:00 by jypeter
