数据透视表问题：错误＆＃39;没有要聚合的数字类型＆＃39;

Question

我无法弄清楚为什么我的数据透视表不起作用，这里是数据透视表和我正在使用的数据样本：

def pivot():
    pivot = pd.pivot_table(clean(),index=['Channel','Advertiser Domain'],values=['eCPM'],columns=['Date'],aggfunc=np.mean)
    return pivot

t = clean()
t.ix[0]
Channel                              COL1
Advertiser Domain         whitecastle.com
Bids                                35483
Imp.                                20336
Avg. Bid CPM (USD)                   8.13
Revenue (USD)                      148.96
eCPM (USD)                           7.33
Wins                                83.97
Date                  2015-04-14 00:00:00
Name: 0, dtype: object

t.info()的输出：

Channel               13601 non-null object
Advertiser Domain     13601 non-null object
Bids                  13601 non-null float64
Imp.                  13601 non-null float64
Avg. Bid CPM (USD)    13601 non-null float64
Revenue (USD)         13601 non-null float64
eCPM (USD)            13601 non-null float64
Wins                  13601 non-null float64
Date                  13601 non-null datetime64[ns]
dtypes: datetime64[ns](1), float64(6), object(2)
memory usage: 1.0+ MB