utils.py 文件源码

def _index_of(arr, lookup):
    """Replace scalars in an array by their indices in a lookup table.

    Implicitely assume that:

    * All elements of arr and lookup are non-negative integers.
    * All elements or arr belong to lookup.

    This is not checked for performance reasons.

    """
    # Equivalent of np.digitize(arr, lookup) - 1, but much faster.
    # TODO: assertions to disable in production for performance reasons.
    # TODO: np.searchsorted(lookup, arr) is faster on small arrays with large
    # values
    lookup = np.asarray(lookup, dtype=np.int32)
    m = (lookup.max() if len(lookup) else 0) + 1
    tmp = np.zeros(m + 1, dtype=np.int)
    # Ensure that -1 values are kept.
    tmp[-1] = -1
    if len(lookup):
        tmp[lookup] = np.arange(len(lookup))
    return tmp[arr]