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other:python:misc_by_jyp [2022/02/21 12:47] jypeter [Sorting] Added link to numpy routines |
other:python:misc_by_jyp [2022/02/21 16:31] jypeter [numpy related stuff] Added ufuncs |
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['c', 'd', 'b', 'a']</code> | ['c', 'd', 'b', 'a']</code> | ||
+ | ==== numpy related stuff ==== | ||
+ | |||
+ | === Finding and counting unique values === | ||
+ | |||
+ | Use ''np.unique'', do **not** try to use histogram related functions! | ||
+ | |||
+ | <code>>>> vals = np.random.randint(2, 5, (10,)) * 0.5 # Get 10 discreet float values | ||
+ | >>> vals | ||
+ | array([1. , 2. , 1. , 2. , 2. , 1.5, 1. , 1.5, 2. , 1.5]) | ||
+ | |||
+ | >>> np.unique(vals) | ||
+ | array([1. , 1.5, 2. ]) | ||
+ | >>> unique_vals, nb_unique = np.unique(vals, return_counts=True) | ||
+ | >>> unique_vals | ||
+ | array([1. , 1.5, 2. ]) | ||
+ | >>> nb_unique | ||
+ | array([3, 3, 4]) | ||
+ | |||
+ | >>> sorted_vals = np.sort(vals) # Sorted copy, in order to check the result | ||
+ | >>> sorted_vals | ||
+ | array([1. , 1. , 1. , 1.5, 1.5, 1.5, 2. , 2. , 2. , 2. ])</code> | ||
+ | |||
+ | === Applying a ufunc over all the elements of an array === | ||
+ | |||
+ | There are all sorts of //ufuncs// (Universal Functions), and we will just use below ''add'' from the [[https://numpy.org/doc/stable/reference/ufuncs.html#math-operations|math operations]], applied on the arrays defined in [[#finding_and_counting_unique_values|Finding and counting unique values]] | ||
+ | |||
+ | <code># Get the sum of all the elements of 'vals' | ||
+ | >>> np.add.reduce(vals) | ||
+ | 15.5 | ||
+ | >>> np.add.reduce(sorted_vals) | ||
+ | 15.5 | ||
+ | >>> vals.sum() # The usual and easy way to do it | ||
+ | 15.5 | ||
+ | |||
+ | # Compute the sum of the elements of 'nb_unique' | ||
+ | # AND keep (accumulate) the intermediate results | ||
+ | >>> nb_unique | ||
+ | array([3, 3, 4]) | ||
+ | >>> np.add.accumulate(nb_unique) | ||
+ | array([ 3, 6, 10]) | ||
+ | |||
+ | # The accumulated values can be used as indices to separate the different groups of sorted values! | ||
+ | >>> sorted_vals | ||
+ | array([1. , 1. , 1. , 1.5, 1.5, 1.5, 2. , 2. , 2. , 2. ]) | ||
+ | >>> sorted_vals[0:3] | ||
+ | array([1., 1., 1.]) | ||
+ | >>> sorted_vals[3:6] | ||
+ | array([1.5, 1.5, 1.5]) | ||
+ | >>> sorted_vals[6:10] | ||
+ | array([2., 2., 2., 2.]) | ||
+ | |||
+ | # Compute the sum of each equal-value group | ||
+ | >>> sorted_vals[0:3].sum(), sorted_vals[3:6].sum(), sorted_vals[6:10].sum() | ||
+ | (3.0, 4.5, 8.0)</code> | ||
/* | /* |