Sortednp

The package to intersect or merge sorted numpy arrays.

Numpy and Numpy arrays are a really great tool. However, intersecting and merging multiple sorted numpy arrays is rather less performant. The current numpy implementation concatenates the two arrays and sorts the combination. If you want to merge or intersect multiple numpy arrays, there is a much faster way, by using the property, that the resulting array is sorted.

Sortednp (sorted numpy) operates on sorted numpy arrays to calculate the intersection or the union of two numpy arrays in an efficient way. The resulting array is again a sorted numpy array, which can be merged or intersected with the next array. The intended use case is that sorted numpy arrays are sorted as the basic data structure and merged or intersected at request. Typical applications include information retrieval and search engines in particular.

It is also possible to implement a k-way merging or intersecting algorithm, which operates on an arbitrary number of arrays at the same time. This package is intended to deal with arrays with $10^6$ or $10^{10}$ items. Usually, these arrays are too large to keep more than two of them in memory at the same time. This package implements methods to merge and intersect multiple arrays, which can be loaded on-demand.

Links

• Git Repository
• Documentation
• PyPI

Installation from PyPI

You can install the package directly from PyPI using pip.

$ pip install sortednp

Numpy Dependency

The installation fails in some cases, because of a build-time dependency on numpy. Usually, the problem can be solved by manually installing a recent numpy version via pip install -U numpy.

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Basic Usage

Two-way intersection

Two sorted numpy arrays can be intersected with the intersect method, which takes two numpy arrays and returns the sorted intersection of the two arrays.

## intersect.py
import numpy as np
import sortednp as snp

a = np.array([0, 3, 4, 6, 7])
b = np.array([1, 2, 3, 5, 7, 9])

i = snp.intersect(a, b)
print(i)

If you run this, you should see the intersection of both arrays as a sorted numpy array.

$ python3 intersect.py
[3 7]

Two-way union

Two numpy sorted arrays can be merged with the merge method, which takes two numpy arrays and returns the sorted union of the two arrays.

## merge.py
import numpy as np
import sortednp as snp

a = np.array([0, 3, 4, 6, 7])
b = np.array([1, 2, 3, 5, 7, 9])

m = snp.merge(a, b)
print(m)

If you run this, you should see the union of both arrays as a sorted numpy array.

$ python3 merge.py
[0 1 2 3 3 4 5 6 7 7 9]