[英]Indexing pandas dataframes inside pandas dataframes with python
我在數據框內有一系列數據框。
頂層數據框的結構如下:
24hr 48hr 72hr
D1 x x x
D2 x x x
D3 x x x
在每種情況下,x都是使用pandas.read_excel()
創建的數據pandas.read_excel()
每個x數據框中的一列標題為“平均容器長度”,並且該列中有三個條目(即行,索引)。
我要返回的是“平均船長”列的平均值。 我也對如何返回該列中的特定單元格感興趣。 我知道有一種用於熊貓數據幀的.mean方法,但是我無法弄清楚使用它的索引語法。
下面是一個例子
import pandas as pd
a = {'Image name' : ['Image 1', 'Image 2', 'Image 3'], 'threshold' : [20, 25, 30], 'Average Vessels Length' : [14.2, 22.6, 15.7] }
b = pd.DataFrame(a, columns=['Image name', 'threshold', 'Average Vessels Length'])
c = pd.DataFrame(index=['D1','D2','D3'], columns=['24hr','48hr','72hr'])
c['24hr']['D1'] = a
c['48hr']['D1'] = a
c['72hr']['D1'] = a
c['24hr']['D2'] = a
c['48hr']['D2'] = a
c['72hr']['D2'] = a
c['24hr']['D3'] = a
c['48hr']['D3'] = a
c['72hr']['D3'] = a
這將返回“平均容器長度”列中的值的平均值:
print b['Average Vessels Length'].mean()
這將返回24小時,D1,“平均船只長度”中的所有值
print c['24hr']['D1']['Average Vessels Length']
這不起作用:
print c['24hr']['D1']['Average Vessels Length'].mean()
而且我不知道如何訪問c ['24hr'] ['D1'] ['平均船只長度']中的任何特定值
最終,我想從Dx ['Average Vessels Length']。mean()的每一列中取平均值,然后將其除以相應的D1 ['Average Vessels Length']。mean()
任何幫助將不勝感激。
我假設既然您說大數據框的每個元素都是一個數據框,那么示例數據應該是:
import pandas as pd
a = {'Image name' : ['Image 1', 'Image 2', 'Image 3'], 'threshold' : [20, 25, 30], 'Average Vessels Length' : [14.2, 22.6, 15.7] }
b = pd.DataFrame(a, columns=['Image name', 'threshold', 'Average Vessels Length'])
c = pd.DataFrame(index=['D1','D2','D3'], columns=['24hr','48hr','72hr'])
c['24hr']['D1'] = b
c['48hr']['D1'] = b
c['72hr']['D1'] = b
c['24hr']['D2'] = b
c['48hr']['D2'] = b
c['72hr']['D2'] = b
c['24hr']['D3'] = b
c['48hr']['D3'] = b
c['72hr']['D3'] = b
要獲取每個單元格的均值,可以使用applymap
,它將函數映射到DataFrame的每個單元格:
cell_means = c.applymap(lambda e: e['Average Vessels Length'].mean())
cell_means
Out[14]:
24hr 48hr 72hr
D1 17.5 17.5 17.5
D2 17.5 17.5 17.5
D3 17.5 17.5 17.5
一旦有了這些喲,就可以得到列均值等,然后繼續以均值歸一化:
col_means = cell_means.mean(axis=0)
col_means
Out[11]:
24hr 17.5
48hr 17.5
72hr 17.5
dtype: float64
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