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前文已经详细介绍DataFrame与Series两种数据结构，下面介绍DataFrame与Series的数据基本手段
一、pandas两种数据结构的index是不可修改的，pandas对象的一个重要方法是reindex
>>> f
lie pop state year
suoyin
a 1.5 ohio 2000
b 1.3 ohio 2001
c 1.7 ohio 2002
d 2.0 nev 2003
e 3.5 nev 2004
>>> f.reindex(list('bcadef'))
lie pop state year
suoyin
b 1.3 ohio 2001.0
c 1.7 ohio 2002.0
a 1.5 ohio 2000.0
d 2.0 nev 2003.0
e 3.5 nev 2004.0
f NaN NaN NaN
>>> f.reindex(list('bcadef'),fill_value=0)#缺失值用0填充
lie pop state year
suoyin
b 1.3 ohio 2001
c 1.7 ohio 2002
a 1.5 ohio 2000
d 2.0 nev 2003
e 3.5 nev 2004
f 0.0 0 0
#method选项对缺失值所插值处理，ffill/pad：前向填充值；bfill/backfill：后向填充值
>>> f.reindex(list('bcadef'),method='ffill')
lie pop state year
suoyin
b 1.3 ohio 2001
c 1.7 ohio 2002
a 1.5 ohio 2000
d 2.0 nev 2003
e 3.5 nev 2004
f 3.5 nev 2004
#DataFrame数据格式，reindex不仅可以修改行索引，也可以修改列。
>>> f.reindex(columns=['pop','year','state','add'])
lie pop year state add
suoyin
a 1.5 2000 ohio NaN
b 1.3 2001 ohio NaN
c 1.7 2002 ohio NaN
d 2.0 2003 nev NaN
e 3.5 2004 nev NaN