Source code for biocutils.union

from typing import Sequence

from .is_missing_scalar import is_missing_scalar
from .map_to_index import DUPLICATE_METHOD




def union(*x: Sequence, duplicate_method: DUPLICATE_METHOD = "first") -> list:
    """
    Identify the union of values in multiple sequences, while preserving the
    order of the first (or last) occurence of each value.

    Args:
        x:
            Zero, one or more sequences of interest containing hashable values.
            We ignore missing values as defined by
            :py:meth:`~biocutils.is_missing_scalar.is_missing_scalar`.

        duplicate_method:
            Whether to take the first or last occurrence of each value in the
            ordering of the output. If first, the first occurrence in the
            earliest sequence of ``x`` is reported; if last, the last
            occurrence in the latest sequence of ``x`` is reported.

    Returns:
        Union of values across all ``x``.
    """

    nargs = len(x)
    if nargs == 0:
        return []

    output = []
    present = set()

    def handler(f):
        if not is_missing_scalar(f) and f not in present:
            output.append(f)
            present.add(f)

    if duplicate_method == "first":
        for a in x:
            for f in a:
                handler(f)
    else:
        for a in reversed(x):
            for f in reversed(a):
                handler(f)
        output.reverse()

    return output