我对访问pandas列的各种方式之间的性能差异感到困惑。
In [1]: df = pd.DataFrame([[1,1,1],[2,2,2]],columns=['a','b','c'])
In [2]: %timeit df['a']
The slowest run took 75.37 times longer than the fastest. This could
mean that an intermediate result is being cached.
100000 loops, best of 3: 3.12 µs per loop
In [3]: %timeit df.a
The slowest run took 5.14 times longer than the fastest. This could
mean that an intermediate result is being cached.
100000 loops, best of 3: 6.59 µs per loop
In [4]: %timeit df.loc[:,'a']
10000 loops, best of 3: 55 µs per loop
据我所知，最后一个变种速度较慢，因为它可以设置值，而不仅仅是访问。但为什么df.a比df['a']慢？无论缓存中间结果如何，这似乎都是正确的。