def val_to_edge(edges, x):
    """Convert axis coordinate to bin index."""
    edges = np.array(edges)
    w = edges[1:] - edges[:-1]
    w = np.insert(w, 0, w[0])
    ibin = np.digitize(np.array(x, ndmin=1), edges - 0.5 * w) - 1
    ibin[ibin < 0] = 0
    return ibin