擅长:python、mysql、java
<p>使用:</p>
<pre><code>df = (df.rename_axis('C2')
.reset_index()
.melt('C2', var_name='C1', value_name='V')
.reindex(columns=['C1','C2','V']))
print (df)
C1 C2 V
0 a a 7
1 a b 0
2 a c 3
3 b a 0
4 b b 4
5 b c 2
6 c a 3
7 c b 2
8 c c 9
</code></pre>