def truncate_start(timeseries, window):
    """
    Truncates a timeseries at the start assuming a moving window was used.
    For example, one might truncate the datetime (x-axis) to start at the
    first tick of a moving average with a given window size.

    Concretely, it splices out the first (window - 1) elements.

    timeseries (list):      timeseries to truncate.
    window (int):           window size.
    """
    return timeseries[-(len(timeseries) - window + 1):]