pandas可以对不同索引的对象进行算术运算，如果存在不同的索引对，结果的索引就是该索引对的并集。
一、算术运算
a、series的加法运算
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s1 = Series([1,2,3],index=["a","b","c"])s2 = Series([4,5,6],index=["a","c","e"])print(s1+s2)'''a 5.0b NaNc 8.0e NaN''' |
sereis相加会自动进行数据对齐操作，在不重叠的索引处会使用NA(NaN)值进行填充，series进行算术运算的时候，不需要保证series的大小一致。
b、DataFrame的加法运算
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d1 = np.arange(1,10).reshape(3,3)dataFrame1 = DataFrame(d1,index=["a","b","c"],columns=["one","two","three"])d2 = np.arange(1,10).reshape(3,3)dataFrame2 = DataFrame(d2,index=["a","b","e"],columns=["one","two","four"])print(dataFrame1+dataFrame2)''' four one three twoa NaN 2.0 NaN 4.0b NaN 8.0 NaN 10.0c NaN NaN NaN NaNe NaN NaN NaN NaN''' |
dataFrame相加时，对齐操作需要行和列的索引都重叠的时候才回相加，否则会使用NA值进行填充。
二、指定填充值
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s1 = Series([1,2,3],index=["a","b","c"])s2 = Series([4,5,6],index=["a","c","e"])print( s1.add(s2,fill_value=0))'''a 5.0b 2.0c 8.0e 6.0''' |
需要注意的时候，使用add方法对两个series进行相加的时候，设置fill_value的值是对于不存在索引的series用指定值进行填充后再进行相加。除了加法add，还有sub减法,div除法,mul乘法，使用方式与add相同。DataFrame与series一样。
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s1 = Series([1,2,3],index=["a","b","c"])s2 = Series([4,5,6],index=["a","c","e"])print(s2.reindex(["a","b","c","d"],fill_value=0))'''a 4b 0c 5d 0'''s3 = s1 + s2print(s3.reindex(["a","b","c","e"],fill_value=0))'''a 5.0b NaNc 8.0e NaN''' |
使用reindex进行填充的时候，需要注意的是，不能对已经是值为NaN的进行重新赋值，只能对使用reindex之前不存在的所以使用指定的填充值，DataFrame也是一样的。
三、DataFrame与Series的混合运算
a、DataFrame的行进行广播
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a = np.arange(9).reshape(3,3)d = DataFrame(a,index=["a","b","c"],columns=["one","two","three"])#取d的第一行为Seriess = d.ix[0]print(d+s)''' one two threea 0 2 4b 3 5 7c 6 8 10''' |
b、DataFrame的列进行广播
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a = np.arange(9).reshape(3,3)d = DataFrame(a,index=["a","b","c"],columns=["one","two","three"])#取d的第一列为Seriess = d["one"]print(d.add(s,axis=0))''' one two threea 0 1 2b 6 7 8c 12 13 14''' |
对列进行广播的时候，必须要使用add方法，而且还要将axis设置为0，不然就会得到下面的结果
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print(d.add(s))''' a b c one three twoa NaN NaN NaN NaN NaN NaNb NaN NaN NaN NaN NaN NaNc NaN NaN NaN NaN NaN NaN''' |
以上这篇对pandas的算术运算和数据对齐实例详解就是小编分享给大家的全部内容了，希望能给大家一个参考，也希望大家多多支持服务器之家。
原文链接：https://blog.csdn.net/sinat_29957455/article/details/78989104
