set_index() pandas

set_index

DataFrame可以通過set_index方法，可以設置單索引和復合索引。 
DataFrame.set_index(keys, drop=True, append=False, inplace=False, verify_integrity=False) 
append添加新索引，drop為False，inplace為True時，索引將會還原為列

In [307]: data
Out[307]: 
     a    b  c    d
0  bar  one  z  1.0
1  bar  two  y  2.0
2  foo  one  x  3.0
3  foo  two  w  4.0

In [308]: indexed1 = data.set_index('c')

In [309]: indexed1
Out[309]: 
     a    b    d
c               
z  bar  one  1.0
y  bar  two  2.0
x  foo  one  3.0
w  foo  two  4.0

In [310]: indexed2 = data.set_index(['a', 'b'])

In [311]: indexed2
Out[311]: 
         c    d
a   b          
bar one  z  1.0
    two  y  2.0
foo one  x  3.0
    two  w  4.0

reset_index

reset_index可以還原索引，從新變為默認的整型索引 
DataFrame.reset_index(level=None, drop=False, inplace=False, col_level=0, col_fill=”) 
level控制了具體要還原的那個等級的索引 
drop為False則索引列會被還原為普通列，否則會丟失

In [318]: data
Out[318]: 
         c    d
a   b          
bar one  z  1.0
    two  y  2.0
foo one  x  3.0
    two  w  4.0

In [319]: data.reset_index()
Out[319]: 
     a    b  c    d
0  bar  one  z  1.0
1  bar  two  y  2.0
2  foo  one  x  3.0
3  foo  two  w  4.0