pandas 获取指定元素所在位置

为了获取所在位置而不是所在索引，对于index推荐使用两种方式index.get_loc(ele)和index.to_list().index(ele)，第一种语句更短，第二种更快

In [1]: import pandas as pd                                                

In [2]: import numpy as np                                                 

In [3]: data = [406400, 203200, 101600,  76100,  50800,  25400,  19050,  12700, 
   ...:          9500,   6700,   4750,   3350,   2360,   1700,   1180,    850, 
   ...:           600,    425,    300,    212,    150,    106,     75,     53, 
   ...:            38]                                                                               

In [4]: myseries = pd.Series(data, index=range(1,26))                                                

In [5]: myseries[21]                                                                                 
Out[5]: 150

In [7]: %timeit myseries[myseries == 150].index[0]                                                   
416 µs ± 5.05 µs per loop (mean ± std. dev. of 7 runs, 1000 loops each)

In [8]: %timeit myseries[myseries == 150].first_valid_index()                                        
585 µs ± 32.5 µs per loop (mean ± std. dev. of 7 runs, 1000 loops each)

In [9]: %timeit myseries.where(myseries == 150).first_valid_index()                                  
652 µs ± 23.3 µs per loop (mean ± std. dev. of 7 runs, 1000 loops each)

In [10]: %timeit myseries.index[np.where(myseries == 150)[0][0]]                                     
195 µs ± 1.18 µs per loop (mean ± std. dev. of 7 runs, 10000 loops each)

In [11]: %timeit pd.Series(myseries.index, index=myseries)[150]                 
178 µs ± 9.35 µs per loop (mean ± std. dev. of 7 runs, 10000 loops each)

In [12]: %timeit myseries.index[pd.Index(myseries).get_loc(150)]                                    
77.4 µs ± 1.41 µs per loop (mean ± std. dev. of 7 runs, 10000 loops each)

In [13]: %timeit myseries.index[list(myseries).index(150)]
12.7 µs ± 42.5 ns per loop (mean ± std. dev. of 7 runs, 100000 loops each)

In [14]: %timeit myseries.index[myseries.tolist().index(150)]                   
9.46 µs ± 19.2 ns per loop (mean ± std. dev. of 7 runs, 100000 loops each)