它只是矩阵乘法：
import pandas as pd
df = pd.read_csv('data.csv',index_col=0, delim_whitespace=True)
df2 = df.applymap(lambda x: int(not pd.isnull(x)))
print df2.T.dot(df2)
输出：
Al01 BBR60 CA07 NL219
Al01 4 0 2 3
BBR60 0 1 0 0
CA07 2 0 3 3
NL219 3 0 3 4
[4 rows x 4 columns]
602392714
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