def FindNotNaNBackwards(x, i):
    """Returns last position (starting at i backwards) which is not NaN, or -1."""
    while i >= 0:
        if not np.isnan(x[i]):
            return i
        i -= 1
    return -1
def FindNotNaNBackwards ( x , i ) : while i >= 0 : if not np . isnan ( x [ i ] ) : return i i -= 1 return - 1
Returns last position (starting at i backwards) which is not NaN, or -1.