pandasで移動平均を求める

サンプルコード

In [3]: arr = [1,2,2,3,4,5,4,19]

In [4]: mea = pd.Series(arr).rolling(window=2).mean()

In [5]: print(mea)
Out[5]: 
0     NaN
1     1.5
2     2.0
3     2.5
4     3.5
5     4.5
6     4.5
7    11.5