A collection of cython-optimized search functions for NumPy

ndfind

A collection of three cython-optimized search functions for NumPy. When the required value is found, they return immediately, without scanning the whole array. It can result in 1000x or larger speedups for huge arrays if the value is located close to the the beginning of the array.

Installation:

pip install ndfind


Contents

Basic usage:

• find(a, v) finds v in a, returns index of the first match or -1 if not found
• first_above(a, v) finds first element in a that is strictly greater than v, returns its index or -1 if not found
• first_nonzero(a) finds the first nonzero element in a, returns its index or -1 if not found

• find(a, v, rtol=1e-05, atol=1e-08, sorted=False, missing=-1, raises=False) Returns the index of the first element in a equal to v. If either a or v (or both) is of floating type, the parameters atol (absolute tolerance) and rtol (relative tolerance) are used for comparison (see np.isclose() for details).

Otherwise, returns the missing value (-1 by default) or raises a ValueError if raises=True.

For example,

    >>> find([3, 1, 4, 1, 5], 4)
2
>>> find([1, 2, 3], 7)
-1
>>> find([1.1, 1.2, 1.3], 1.2)
1
>>> find(np.arange(0, 1, 0.1), 0.3)
3
>>> find([[3, 8, 4], [5, 2, 7]], 7)
(1, 2)
>>> find([[3, 8, 4], [5, 2, 7]], 9)
-1
>>> find([999980., 999990., 1e6], 1e6)
1
>>> find([999980., 999990., 1e6], 1e6, rtol=1e-9)
2

• first_above(a, v, sorted=False, missing=-1, raises=False) Returns the index of the first element in a strictly greater than v. If either a or v (or both) is of floating type, the parameters atol (absolute tolerance) and rtol (relative tolerance) are used for comparison (see np.isclose() for details).

In 2D and above the the values in a are always tested and returned in row-major, C-style order.

If there is no value in a greater than v, returns the default value (-1 by default) or raises a ValueError if raises=True.

sorted, use binary search to speed things up (works only if the array is sorted)

For example,

    >>> first_above([4, 5, 8, 2, 7], 6)
2
>>> first_above([[4, 5, 8], [2, 7, 3]], 6)
(0, 2)
>>> first_above([5, 6, 7], 9)
3

• first_nonzero(a, missing=-1, raises=False) Returns the index of the first nonzero element in a.

In 2D and above the the values in a are always tested and returned in row-major, C-style order.

For example,

>>> first_nonzero([0, 0, 7, 0, 5])
2
>>> first_nonzero([False, True, False, False, True])
1
>>> first_nonzero([[0, 0, 0, 0], [0, 0, 5, 3]])
(1, 2)


Testing

Run pytest in the project root.

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