Function transform 

pub fn transform<F, G, Iter>(
    input_batch_size: usize,
    partitions_per_thread: usize,
    graph: G,
    transformation: F,
    target_path: PathBuf,
) -> Result<()>
where
    F: Fn(usize, usize) -> Iter + Send + Sync,
    Iter: IntoIterator<Item = (usize, usize), IntoIter: Send + Sync>,
    G: SplitLabeling<Label = usize>,
    for<'a> <<G as SplitLabeling>::IntoIterator<'a> as IntoIterator>::IntoIter: Send + Sync,
    for<'a, 'b> <<<G as SplitLabeling>::SplitLender<'a> as NodeLabelsLender<'b>>::IntoIterator as IntoIterator>::IntoIter: Send + Sync,

Writes a new graph on disk, obtained by applying the function to all arcs on the source graph.