10分钟Pandas教程
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10 Minutes to pandas
10分钟pandas教程
对于数据处理分析的新手,花十分钟熟悉pandas很有必要,一起开始吧~
第一步要会导入pandas和其好基友们:
In [1]: import pandas as pdIn [2]: import numpy as npIn [3]: import matplotlib.pyplot as plt
对象创建
本节可以具体参考Data Structure Intro section。
通过传入一个list的值来创建一个Series
,并让pandas创建一个默认的序号索引:
In [4]: s = pd.Series([1,3,5,np.nan,6,8])In [5]: sOut[5]: 0 1.01 3.02 5.03 NaN4 6.05 8.0dtype: float64
通过传入一个numpy数组,创建一个DataFrame
,并以时间为索引以列为标签:
In [6]: dates = pd.date_range('20130101', periods=6)In [7]: datesOut[7]: DatetimeIndex(['2013-01-01', '2013-01-02', '2013-01-03', '2013-01-04', '2013-01-05', '2013-01-06'], dtype='datetime64[ns]', freq='D')In [8]: df = pd.DataFrame(np.random.randn(6,4), index=dates, columns=list('ABCD'))In [9]: dfOut[9]: A B C D2013-01-01 0.469112 -0.282863 -1.509059 -1.1356322013-01-02 1.212112 -0.173215 0.119209 -1.0442362013-01-03 -0.861849 -2.104569 -0.494929 1.0718042013-01-04 0.721555 -0.706771 -1.039575 0.2718602013-01-05 -0.424972 0.567020 0.276232 -1.0874012013-01-06 -0.673690 0.113648 -1.478427 0.524988
通过字典(dict
)传入的对象而创建的DataFrame
可以转为series
样式:
In [10]: df2 = pd.DataFrame({ 'A' : 1., ....: 'B' : pd.Timestamp('20130102'), ....: 'C' : pd.Series(1,index=list(range(4)),dtype='float32'), ....: 'D' : np.array([3] * 4,dtype='int32'), ....: 'E' : pd.Categorical(["test","train","test","train"]), ....: 'F' : 'foo' }) ....: In [11]: df2Out[11]: A B C D E F0 1.0 2013-01-02 1.0 3 test foo1 1.0 2013-01-02 1.0 3 train foo2 1.0 2013-01-02 1.0 3 test foo3 1.0 2013-01-02 1.0 3 train foo
其数据类型(dtypes
)分别为:
In [12]: df2.dtypesOut[12]: A float64B datetime64[ns]C float32D int32E categoryF objectdtype: object
如果你在使用IPython,利用Tab键的自动补全会得到所有的列名称(除此外也有其他的公共属性):
In [13]: df2.<TAB>df2.A df2.booldf2.abs df2.boxplotdf2.add df2.Cdf2.add_prefix df2.clipdf2.add_suffix df2.clip_lowerdf2.align df2.clip_upperdf2.all df2.columnsdf2.any df2.combinedf2.append df2.combine_firstdf2.apply df2.compounddf2.applymap df2.consolidatedf2.as_blocks df2.convert_objectsdf2.asfreq df2.copydf2.as_matrix df2.corrdf2.astype df2.corrwithdf2.at df2.countdf2.at_time df2.covdf2.axes df2.cummaxdf2.B df2.cummindf2.between_time df2.cumproddf2.bfill df2.cumsumdf2.blocks df2.D
如你所见,A,B,C,D
都被补全了,E
也存在,但为了简洁被截断显示了。
浏览数据
详情参见Basics section。
查看frame中顶部和尾部行的数据:
In [14]: df.head()Out[14]: A B C D2013-01-01 0.469112 -0.282863 -1.509059 -1.1356322013-01-02 1.212112 -0.173215 0.119209 -1.0442362013-01-03 -0.861849 -2.104569 -0.494929 1.0718042013-01-04 0.721555 -0.706771 -1.039575 0.2718602013-01-05 -0.424972 0.567020 0.276232 -1.087401In [15]: df.tail(3)Out[15]: A B C D2013-01-04 0.721555 -0.706771 -1.039575 0.2718602013-01-05 -0.424972 0.567020 0.276232 -1.0874012013-01-06 -0.673690 0.113648 -1.478427 0.524988
显示索引,列标签,以及numpy格式的数据:
In [16]: df.indexOut[16]: DatetimeIndex(['2013-01-01', '2013-01-02', '2013-01-03', '2013-01-04', '2013-01-05', '2013-01-06'], dtype='datetime64[ns]', freq='D')In [17]: df.columnsOut[17]: Index(['A', 'B', 'C', 'D'], dtype='object')In [18]: df.valuesOut[18]: array([[ 0.4691, -0.2829, -1.5091, -1.1356], [ 1.2121, -0.1732, 0.1192, -1.0442], [-0.8618, -2.1046, -0.4949, 1.0718], [ 0.7216, -0.7068, -1.0396, 0.2719], [-0.425 , 0.567 , 0.2762, -1.0874], [-0.6737, 0.1136, -1.4784, 0.525 ]])
对数据进行快速总结:
In [19]: df.describe()Out[19]: A B C Dcount 6.000000 6.000000 6.000000 6.000000mean 0.073711 -0.431125 -0.687758 -0.233103std 0.843157 0.922818 0.779887 0.973118min -0.861849 -2.104569 -1.509059 -1.13563225% -0.611510 -0.600794 -1.368714 -1.07661050% 0.022070 -0.228039 -0.767252 -0.38618875% 0.658444 0.041933 -0.034326 0.461706max 1.212112 0.567020 0.276232 1.071804
转置数据:
In [20]: df.TOut[20]: 2013-01-01 2013-01-02 2013-01-03 2013-01-04 2013-01-05 2013-01-06A 0.469112 1.212112 -0.861849 0.721555 -0.424972 -0.673690B -0.282863 -0.173215 -2.104569 -0.706771 0.567020 0.113648C -1.509059 0.119209 -0.494929 -1.039575 0.276232 -1.478427D -1.135632 -1.044236 1.071804 0.271860 -1.087401 0.524988
按某一轴进行排序:
In [21]: df.sort_index(axis=1, ascending=False)Out[21]: D C B A2013-01-01 -1.135632 -1.509059 -0.282863 0.4691122013-01-02 -1.044236 0.119209 -0.173215 1.2121122013-01-03 1.071804 -0.494929 -2.104569 -0.8618492013-01-04 0.271860 -1.039575 -0.706771 0.7215552013-01-05 -1.087401 0.276232 0.567020 -0.4249722013-01-06 0.524988 -1.478427 0.113648 -0.673690
按值排序:
In [22]: df.sort_values(by='B')Out[22]: A B C D2013-01-03 -0.861849 -2.104569 -0.494929 1.0718042013-01-04 0.721555 -0.706771 -1.039575 0.2718602013-01-01 0.469112 -0.282863 -1.509059 -1.1356322013-01-02 1.212112 -0.173215 0.119209 -1.0442362013-01-06 -0.673690 0.113648 -1.478427 0.5249882013-01-05 -0.424972 0.567020 0.276232 -1.087401
选择
注意: 虽然使用标准的Python/Numpy表达式进行选择和赋值是直观的,可以用于交互式工作,但对于生成代码,我们建议使用优化过的pandas数据访问方法:
.at
,.iat
,.loc
,.iloc
和.ix
。
获取
选择单独一列,返回一个Series
,和df.A
等同:
In [23]: df['A']Out[23]: 2013-01-01 0.4691122013-01-02 1.2121122013-01-03 -0.8618492013-01-04 0.7215552013-01-05 -0.4249722013-01-06 -0.673690Freq: D, Name: A, dtype: float64
使用[]
选择,对行进行切片:
In [24]: df[0:3]Out[24]: A B C D2013-01-01 0.469112 -0.282863 -1.509059 -1.1356322013-01-02 1.212112 -0.173215 0.119209 -1.0442362013-01-03 -0.861849 -2.104569 -0.494929 1.071804In [25]: df['20130102':'20130104']Out[25]: A B C D2013-01-02 1.212112 -0.173215 0.119209 -1.0442362013-01-03 -0.861849 -2.104569 -0.494929 1.0718042013-01-04 0.721555 -0.706771 -1.039575 0.271860
用标签选择
参见Selection by Label。
使用标签选择得到一个交叉项:
In [26]: df.loc[dates[0]]Out[26]: A 0.469112B -0.282863C -1.509059D -1.135632Name: 2013-01-01 00:00:00, dtype: float64
使用标签选择多个轴:
In [27]: df.loc[:,['A','B']]Out[27]: A B2013-01-01 0.469112 -0.2828632013-01-02 1.212112 -0.1732152013-01-03 -0.861849 -2.1045692013-01-04 0.721555 -0.7067712013-01-05 -0.424972 0.5670202013-01-06 -0.673690 0.113648
显示标签切片,起止点都被包括在内:
In [28]: df.loc['20130102':'20130104',['A','B']]Out[28]: A B2013-01-02 1.212112 -0.1732152013-01-03 -0.861849 -2.1045692013-01-04 0.721555 -0.706771
减少返回对象的维度:
In [29]: df.loc['20130102',['A','B']]Out[29]: A 1.212112B -0.173215Name: 2013-01-02 00:00:00, dtype: float64
得到一个标量:
In [30]: df.loc[dates[0],'A']Out[30]: 0.46911229990718628
更快的速度!(和上面的方法一样)
In [31]: df.at[dates[0],'A']Out[31]: 0.46911229990718628
以位置选择
更多参见:Selection by Position
通过传入整数位置进行选择
In [32]: df.iloc[3]Out[32]: A 0.721555B -0.706771C -1.039575D 0.271860Name: 2013-01-04 00:00:00, dtype: float64
通过整数切片,和numpy、python的操作类似
In [33]: df.iloc[3:5,0:2]Out[33]: A B2013-01-04 0.721555 -0.7067712013-01-05 -0.424972 0.567020
通过整数位置坐标,和numpy、python的风格类似:
In [34]: df.iloc[[1,2,4],[0,2]]Out[34]: A C2013-01-02 1.212112 0.1192092013-01-03 -0.861849 -0.4949292013-01-05 -0.424972 0.276232
行切片:
In [35]: df.iloc[1:3,:]Out[35]: A B C D2013-01-02 1.212112 -0.173215 0.119209 -1.0442362013-01-03 -0.861849 -2.104569 -0.494929 1.071804
列切片:
In [36]: df.iloc[:,1:3]Out[36]: B C2013-01-01 -0.282863 -1.5090592013-01-02 -0.173215 0.1192092013-01-03 -2.104569 -0.4949292013-01-04 -0.706771 -1.0395752013-01-05 0.567020 0.2762322013-01-06 0.113648 -1.478427
获得某一点的值:
In [37]: df.iloc[1,1]Out[37]: -0.17321464905330858
更快的方法!
In [38]: df.iat[1,1]Out[38]: -0.17321464905330858
布尔值索引
使用单个列的(布尔)值进行选择:
In [39]: df[df.A > 0]Out[39]: A B C D2013-01-01 0.469112 -0.282863 -1.509059 -1.1356322013-01-02 1.212112 -0.173215 0.119209 -1.0442362013-01-04 0.721555 -0.706771 -1.039575 0.271860
从一个DataFrame中,选择满足布尔条件的值:
In [40]: df[df > 0]Out[40]: A B C D2013-01-01 0.469112 NaN NaN NaN2013-01-02 1.212112 NaN 0.119209 NaN2013-01-03 NaN NaN NaN 1.0718042013-01-04 0.721555 NaN NaN 0.2718602013-01-05 NaN 0.567020 0.276232 NaN2013-01-06 NaN 0.113648 NaN 0.524988
使用isin()方法进行过滤:
In [41]: df2 = df.copy()In [42]: df2['E'] = ['one', 'one','two','three','four','three']In [43]: df2Out[43]: A B C D E2013-01-01 0.469112 -0.282863 -1.509059 -1.135632 one2013-01-02 1.212112 -0.173215 0.119209 -1.044236 one2013-01-03 -0.861849 -2.104569 -0.494929 1.071804 two2013-01-04 0.721555 -0.706771 -1.039575 0.271860 three2013-01-05 -0.424972 0.567020 0.276232 -1.087401 four2013-01-06 -0.673690 0.113648 -1.478427 0.524988 threeIn [44]: df2[df2['E'].isin(['two','four'])]Out[44]: A B C D E2013-01-03 -0.861849 -2.104569 -0.494929 1.071804 two2013-01-05 -0.424972 0.567020 0.276232 -1.087401 four
赋值
创建一个新的列,并自动使数据与索引对齐
In [45]: s1 = pd.Series([1,2,3,4,5,6], index=pd.date_range('20130102', periods=6))In [46]: s1Out[46]: 2013-01-02 12013-01-03 22013-01-04 32013-01-05 42013-01-06 52013-01-07 6Freq: D, dtype: int64In [47]: df['F'] = s1
通过标签赋值:
In [48]: df.at[dates[0],'A'] = 0
通过位置赋值:
In [49]: df.iat[0,1] = 0
通过指定的numpy数组赋值:
In [50]: df.loc[:,'D'] = np.array([5] * len(df))In [51]: dfOut[51]: A B C D F2013-01-01 0.000000 0.000000 -1.509059 5 NaN2013-01-02 1.212112 -0.173215 0.119209 5 1.02013-01-03 -0.861849 -2.104569 -0.494929 5 2.02013-01-04 0.721555 -0.706771 -1.039575 5 3.02013-01-05 -0.424972 0.567020 0.276232 5 4.02013-01-06 -0.673690 0.113648 -1.478427 5 5.0
使用where
操作赋值:
In [52]: df2 = df.copy()In [53]: df2[df2 > 0] = -df2In [54]: df2Out[54]: A B C D F2013-01-01 0.000000 0.000000 -1.509059 -5 NaN2013-01-02 -1.212112 -0.173215 -0.119209 -5 -1.02013-01-03 -0.861849 -2.104569 -0.494929 -5 -2.02013-01-04 -0.721555 -0.706771 -1.039575 -5 -3.02013-01-05 -0.424972 -0.567020 -0.276232 -5 -4.02013-01-06 -0.673690 -0.113648 -1.478427 -5 -5.0
缺失数据
pandas主要使用np.nan
来表示缺失的数据。它默认不被计算所包括。详见:Missing Data section。
重新索引允许更改/添加/删除指定轴上的索引。 这将返回该数据的副本。
In [55]: df1 = df.reindex(index=dates[0:4], columns=list(df.columns) + ['E'])In [56]: df1.loc[dates[0]:dates[1],'E'] = 1In [57]: df1Out[57]: A B C D F E2013-01-01 0.000000 0.000000 -1.509059 5 NaN 1.02013-01-02 1.212112 -0.173215 0.119209 5 1.0 1.02013-01-03 -0.861849 -2.104569 -0.494929 5 2.0 NaN2013-01-04 0.721555 -0.706771 -1.039575 5 3.0 NaN
丢弃任意拥有缺失数据的列:
In [58]: df1.dropna(how='any')Out[58]: A B C D F E2013-01-02 1.212112 -0.173215 0.119209 5 1.0 1.0
填充缺失数据:
In [59]: df1.fillna(value=5)Out[59]: A B C D F E2013-01-01 0.000000 0.000000 -1.509059 5 5.0 1.02013-01-02 1.212112 -0.173215 0.119209 5 1.0 1.02013-01-03 -0.861849 -2.104569 -0.494929 5 2.0 5.02013-01-04 0.721555 -0.706771 -1.039575 5 3.0 5.0
获得布尔值掩模当数据为nan
时:
In [60]: pd.isnull(df1)Out[60]: A B C D F E2013-01-01 False False False False True False2013-01-02 False False False False False False2013-01-03 False False False False False True2013-01-04 False False False False False True
操作:
详见Basic section on Binary Ops
统计值
通常情况下不包括缺失数据。
描述性统计:
In [61]: df.mean()Out[61]: A -0.004474B -0.383981C -0.687758D 5.000000F 3.000000dtype: float64
对某一轴进行同样的操作:
In [62]: df.mean(1)Out[62]: 2013-01-01 0.8727352013-01-02 1.4316212013-01-03 0.7077312013-01-04 1.3950422013-01-05 1.8836562013-01-06 1.592306Freq: D, dtype: float64
对于拥有不同维度的对象,操作需要进行对齐。pandas会自动沿着选定的维度进行broadcasts
。
In [63]: s = pd.Series([1,3,5,np.nan,6,8], index=dates).shift(2)In [64]: sOut[64]: 2013-01-01 NaN2013-01-02 NaN2013-01-03 1.02013-01-04 3.02013-01-05 5.02013-01-06 NaNFreq: D, dtype: float64In [65]: df.sub(s, axis='index')Out[65]: A B C D F2013-01-01 NaN NaN NaN NaN NaN2013-01-02 NaN NaN NaN NaN NaN2013-01-03 -1.861849 -3.104569 -1.494929 4.0 1.02013-01-04 -2.278445 -3.706771 -4.039575 2.0 0.02013-01-05 -5.424972 -4.432980 -4.723768 0.0 -1.02013-01-06 NaN NaN NaN NaN NaN
应用
对数据应用函数:
In [66]: df.apply(np.cumsum)Out[66]: A B C D F2013-01-01 0.000000 0.000000 -1.509059 5 NaN2013-01-02 1.212112 -0.173215 -1.389850 10 1.02013-01-03 0.350263 -2.277784 -1.884779 15 3.02013-01-04 1.071818 -2.984555 -2.924354 20 6.02013-01-05 0.646846 -2.417535 -2.648122 25 10.02013-01-06 -0.026844 -2.303886 -4.126549 30 15.0In [67]: df.apply(lambda x: x.max() - x.min())Out[67]: A 2.073961B 2.671590C 1.785291D 0.000000F 4.000000dtype: float64
直方图
详见直方图Histogramming and Discretization。
In [68]: s = pd.Series(np.random.randint(0, 7, size=10))In [69]: sOut[69]: 0 41 22 13 24 65 46 47 68 49 4dtype: int64In [70]: s.value_counts()Out[70]: 4 56 22 21 1dtype: int64
字符串方法
series 在 str
属性中具有许多操作,模式匹配通常使用正则表达式。更多参见 Vectorized String Methods。
In [71]: s = pd.Series(['A', 'B', 'C', 'Aaba', 'Baca', np.nan, 'CABA', 'dog', 'cat'])In [72]: s.str.lower()Out[72]: 0 a1 b2 c3 aaba4 baca5 NaN6 caba7 dog8 catdtype: object
合并
连接
pandas提供了多种利用逻辑关系合并 Series, DataFrame, 和 Panel 对象的简易方法。详见Merging section。
连接pandas对象使用concat()。
In [73]: df = pd.DataFrame(np.random.randn(10, 4))In [74]: dfOut[74]: 0 1 2 30 -0.548702 1.467327 -1.015962 -0.4830751 1.637550 -1.217659 -0.291519 -1.7455052 -0.263952 0.991460 -0.919069 0.2660463 -0.709661 1.669052 1.037882 -1.7057754 -0.919854 -0.042379 1.247642 -0.0099205 0.290213 0.495767 0.362949 1.5481066 -1.131345 -0.089329 0.337863 -0.9458677 -0.932132 1.956030 0.017587 -0.0166928 -0.575247 0.254161 -1.143704 0.2158979 1.193555 -0.077118 -0.408530 -0.862495# break it into piecesIn [75]: pieces = [df[:3], df[3:7], df[7:]]In [76]: pd.concat(pieces)Out[76]: 0 1 2 30 -0.548702 1.467327 -1.015962 -0.4830751 1.637550 -1.217659 -0.291519 -1.7455052 -0.263952 0.991460 -0.919069 0.2660463 -0.709661 1.669052 1.037882 -1.7057754 -0.919854 -0.042379 1.247642 -0.0099205 0.290213 0.495767 0.362949 1.5481066 -1.131345 -0.089329 0.337863 -0.9458677 -0.932132 1.956030 0.017587 -0.0166928 -0.575247 0.254161 -1.143704 0.2158979 1.193555 -0.077118 -0.408530 -0.862495
加入
SQL式的合并。参见Database style joining
In [77]: left = pd.DataFrame({'key': ['foo', 'foo'], 'lval': [1, 2]})In [78]: right = pd.DataFrame({'key': ['foo', 'foo'], 'rval': [4, 5]})In [79]: leftOut[79]: key lval0 foo 11 foo 2In [80]: rightOut[80]: key rval0 foo 41 foo 5In [81]: pd.merge(left, right, on='key')Out[81]: key lval rval0 foo 1 41 foo 1 52 foo 2 43 foo 2 5
添加
在Dataframe上添加一行。详见 Appending。
In [87]: df = pd.DataFrame(np.random.randn(8, 4), columns=['A','B','C','D'])In [88]: dfOut[88]: A B C D0 1.346061 1.511763 1.627081 -0.9905821 -0.441652 1.211526 0.268520 0.0245802 -1.577585 0.396823 -0.105381 -0.5325323 1.453749 1.208843 -0.080952 -0.2646104 -0.727965 -0.589346 0.339969 -0.6932055 -0.339355 0.593616 0.884345 1.5914316 0.141809 0.220390 0.435589 0.1924517 -0.096701 0.803351 1.715071 -0.708758In [89]: s = df.iloc[3]In [90]: df.append(s, ignore_index=True)Out[90]: A B C D0 1.346061 1.511763 1.627081 -0.9905821 -0.441652 1.211526 0.268520 0.0245802 -1.577585 0.396823 -0.105381 -0.5325323 1.453749 1.208843 -0.080952 -0.2646104 -0.727965 -0.589346 0.339969 -0.6932055 -0.339355 0.593616 0.884345 1.5914316 0.141809 0.220390 0.435589 0.1924517 -0.096701 0.803351 1.715071 -0.7087588 1.453749 1.208843 -0.080952 -0.264610
分组
分组指的是以下一或多个步骤:
- 分割 按不同的规则分割数据
- 应用 对每组应用不同的函数
- 结合 将结果结合到一个数据类型
详见Grouping section
In [91]: df = pd.DataFrame({'A' : ['foo', 'bar', 'foo', 'bar', ....: 'foo', 'bar', 'foo', 'foo'], ....: 'B' : ['one', 'one', 'two', 'three', ....: 'two', 'two', 'one', 'three'], ....: 'C' : np.random.randn(8), ....: 'D' : np.random.randn(8)}) ....: In [92]: dfOut[92]: A B C D0 foo one -1.202872 -0.0552241 bar one -1.814470 2.3959852 foo two 1.018601 1.5528253 bar three -0.595447 0.1665994 foo two 1.395433 0.0476095 bar two -0.392670 -0.1364736 foo one 0.007207 -0.5617577 foo three 1.928123 -1.623033
使用sum
函数对分组对象进行求和。
In [93]: df.groupby('A').sum()Out[93]: C DA bar -2.802588 2.42611foo 3.146492 -0.63958
使用多个列标签进行分组:
In [94]: df.groupby(['A','B']).sum()Out[94]: C DA B bar one -1.814470 2.395985 three -0.595447 0.166599 two -0.392670 -0.136473foo one -1.195665 -0.616981 three 1.928123 -1.623033 two 2.414034 1.600434
变形
详见Hierarchical Indexing 和 Reshaping。
Stack
In [95]: tuples = list(zip(*[['bar', 'bar', 'baz', 'baz', ....: 'foo', 'foo', 'qux', 'qux'], ....: ['one', 'two', 'one', 'two', ....: 'one', 'two', 'one', 'two']])) ....: In [96]: index = pd.MultiIndex.from_tuples(tuples, names=['first', 'second'])In [97]: df = pd.DataFrame(np.random.randn(8, 2), index=index, columns=['A', 'B'])In [98]: df2 = df[:4]In [99]: df2Out[99]: A Bfirst second bar one 0.029399 -0.542108 two 0.282696 -0.087302baz one -1.575170 1.771208 two 0.816482 1.100230
stack()方法将DataFrame压缩为一列。
In [100]: stacked = df2.stack()In [101]: stackedOut[101]: first second bar one A 0.029399 B -0.542108 two A 0.282696 B -0.087302baz one A -1.575170 B 1.771208 two A 0.816482 B 1.100230dtype: float64
逆操作为 unstack()。
In [102]: stacked.unstack()Out[102]: A Bfirst second bar one 0.029399 -0.542108 two 0.282696 -0.087302baz one -1.575170 1.771208 two 0.816482 1.100230In [103]: stacked.unstack(1)Out[103]: second one twofirst bar A 0.029399 0.282696 B -0.542108 -0.087302baz A -1.575170 0.816482 B 1.771208 1.100230In [104]: stacked.unstack(0)Out[104]: first bar bazsecond one A 0.029399 -1.575170 B -0.542108 1.771208two A 0.282696 0.816482 B -0.087302 1.100230
数据透视表
详见 Pivot Tables。
In [105]: df = pd.DataFrame({'A' : ['one', 'one', 'two', 'three'] * 3, .....: 'B' : ['A', 'B', 'C'] * 4, .....: 'C' : ['foo', 'foo', 'foo', 'bar', 'bar', 'bar'] * 2, .....: 'D' : np.random.randn(12), .....: 'E' : np.random.randn(12)}) .....: In [106]: dfOut[106]: A B C D E0 one A foo 1.418757 -0.1796661 one B foo -1.879024 1.2918362 two C foo 0.536826 -0.0096143 three A bar 1.006160 0.3921494 one B bar -0.029716 0.2645995 one C bar -1.146178 -0.0574096 two A foo 0.100900 -1.4256387 three B foo -1.035018 1.0240988 one C foo 0.314665 -0.1060629 one A bar -0.773723 1.82437510 two B bar -1.170653 0.59597411 three C bar 0.648740 1.167115
可以很简单地产生透视表:
In [107]: pd.pivot_table(df, values='D', index=['A', 'B'], columns=['C'])Out[107]: C bar fooA B one A -0.773723 1.418757 B -0.029716 -1.879024 C -1.146178 0.314665three A 1.006160 NaN B NaN -1.035018 C 0.648740 NaNtwo A NaN 0.100900 B -1.170653 NaN C NaN 0.536826
时间序列
pandas具有简单、强大以及有效的时间序列函数,详见Time Series section。
In [108]: rng = pd.date_range('1/1/2012', periods=100, freq='S')In [109]: ts = pd.Series(np.random.randint(0, 500, len(rng)), index=rng)In [110]: ts.resample('5Min').sum()Out[110]: 2012-01-01 25083Freq: 5T, dtype: int64
时区转换:
In [111]: rng = pd.date_range('3/6/2012 00:00', periods=5, freq='D')In [112]: ts = pd.Series(np.random.randn(len(rng)), rng)In [113]: tsOut[113]: 2012-03-06 0.4640002012-03-07 0.2273712012-03-08 -0.4969222012-03-09 0.3063892012-03-10 -2.290613Freq: D, dtype: float64In [114]: ts_utc = ts.tz_localize('UTC')In [115]: ts_utcOut[115]: 2012-03-06 00:00:00+00:00 0.4640002012-03-07 00:00:00+00:00 0.2273712012-03-08 00:00:00+00:00 -0.4969222012-03-09 00:00:00+00:00 0.3063892012-03-10 00:00:00+00:00 -2.290613Freq: D, dtype: float64
转为另一个时区
In [116]: ts_utc.tz_convert('US/Eastern')Out[116]: 2012-03-05 19:00:00-05:00 0.4640002012-03-06 19:00:00-05:00 0.2273712012-03-07 19:00:00-05:00 -0.4969222012-03-08 19:00:00-05:00 0.3063892012-03-09 19:00:00-05:00 -2.290613Freq: D, dtype: float64
时区跨度表示:
In [117]: rng = pd.date_range('1/1/2012', periods=5, freq='M')In [118]: ts = pd.Series(np.random.randn(len(rng)), index=rng)In [119]: tsOut[119]: 2012-01-31 -1.1346232012-02-29 -1.5618192012-03-31 -0.2608382012-04-30 0.2819572012-05-31 1.523962Freq: M, dtype: float64In [120]: ps = ts.to_period()In [121]: psOut[121]: 2012-01 -1.1346232012-02 -1.5618192012-03 -0.2608382012-04 0.2819572012-05 1.523962Freq: M, dtype: float64In [122]: ps.to_timestamp()Out[122]: 2012-01-01 -1.1346232012-02-01 -1.5618192012-03-01 -0.2608382012-04-01 0.2819572012-05-01 1.523962Freq: MS, dtype: float64
周期和时间戳的转换让算数函数变得方便。
In [123]: prng = pd.period_range('1990Q1', '2000Q4', freq='Q-NOV')In [124]: ts = pd.Series(np.random.randn(len(prng)), prng)In [125]: ts.index = (prng.asfreq('M', 'e') + 1).asfreq('H', 's') + 9In [126]: ts.head()Out[126]: 1990-03-01 09:00 -0.9029371990-06-01 09:00 0.0681591990-09-01 09:00 -0.0578731990-12-01 09:00 -0.3682041991-03-01 09:00 -1.144073Freq: H, dtype: float64
分类
从0.15版本开始,pandas可以在DataFrame
中支持Categorical类型的数据,详细 介绍参看:categorical introduction和API documentation。
In [127]: df = pd.DataFrame({"id":[1,2,3,4,5,6], "raw_grade":['a', 'b', 'b', 'a', 'a', 'e']})
把原始等级转为分类类型。
In [128]: df["grade"] = df["raw_grade"].astype("category")In [129]: df["grade"]Out[129]: 0 a1 b2 b3 a4 a5 eName: grade, dtype: categoryCategories (3, object): [a, b, e]
重命名类名:
In [130]: df["grade"].cat.categories = ["very good", "good", "very bad"]
分类重新排序:
In [131]: df["grade"] = df["grade"].cat.set_categories(["very bad", "bad", "medium", "good", "very good"])In [132]: df["grade"]Out[132]: 0 very good1 good2 good3 very good4 very good5 very badName: grade, dtype: categoryCategories (5, object): [very bad, bad, medium, good, very good]
数据以类别排序:
In [133]: df.sort_values(by="grade")Out[133]: id raw_grade grade5 6 e very bad1 2 b good2 3 b good0 1 a very good3 4 a very good4 5 a very good
使用分组并包括空目录分类:
In [134]: df.groupby("grade").size()Out[134]: gradevery bad 1bad 0medium 0good 2very good 3dtype: int64
绘图
绘图文档参见Plotting
In [135]: ts = pd.Series(np.random.randn(1000), index=pd.date_range('1/1/2000', periods=1000))In [136]: ts = ts.cumsum()In [137]: ts.plot()Out[137]: <matplotlib.axes._subplots.AxesSubplot at 0x1187d7278>
在DataFrame中,plot()是一种以列为标签绘图的简单方法。
In [138]: df = pd.DataFrame(np.random.randn(1000, 4), index=ts.index, .....: columns=['A', 'B', 'C', 'D']) .....: In [139]: df = df.cumsum()In [140]: plt.figure(); df.plot(); plt.legend(loc='best')Out[140]: <matplotlib.legend.Legend at 0x11b5dea20>
Getting Data In/Out
CSV
写一个csv文件。
In [141]: df.to_csv('foo.csv')
读一个csv文件。
In [142]: pd.read_csv('foo.csv')Out[142]: Unnamed: 0 A B C D0 2000-01-01 0.266457 -0.399641 -0.219582 1.1868601 2000-01-02 -1.170732 -0.345873 1.653061 -0.2829532 2000-01-03 -1.734933 0.530468 2.060811 -0.5155363 2000-01-04 -1.555121 1.452620 0.239859 -1.1568964 2000-01-05 0.578117 0.511371 0.103552 -2.4282025 2000-01-06 0.478344 0.449933 -0.741620 -1.9624096 2000-01-07 1.235339 -0.091757 -1.543861 -1.084753.. ... ... ... ... ...993 2002-09-20 -10.628548 -9.153563 -7.883146 28.313940994 2002-09-21 -10.390377 -8.727491 -6.399645 30.914107995 2002-09-22 -8.985362 -8.485624 -4.669462 31.367740996 2002-09-23 -9.558560 -8.781216 -4.499815 30.518439997 2002-09-24 -9.902058 -9.340490 -4.386639 30.105593998 2002-09-25 -10.216020 -9.480682 -3.933802 29.758560999 2002-09-26 -11.856774 -10.671012 -3.216025 29.369368[1000 rows x 5 columns]
HDF5
读写HDFStores。
写:
In [143]: df.to_hdf('foo.h5','df')
读:
In [144]: pd.read_hdf('foo.h5','df')Out[144]: A B C D2000-01-01 0.266457 -0.399641 -0.219582 1.1868602000-01-02 -1.170732 -0.345873 1.653061 -0.2829532000-01-03 -1.734933 0.530468 2.060811 -0.5155362000-01-04 -1.555121 1.452620 0.239859 -1.1568962000-01-05 0.578117 0.511371 0.103552 -2.4282022000-01-06 0.478344 0.449933 -0.741620 -1.9624092000-01-07 1.235339 -0.091757 -1.543861 -1.084753... ... ... ... ...2002-09-20 -10.628548 -9.153563 -7.883146 28.3139402002-09-21 -10.390377 -8.727491 -6.399645 30.9141072002-09-22 -8.985362 -8.485624 -4.669462 31.3677402002-09-23 -9.558560 -8.781216 -4.499815 30.5184392002-09-24 -9.902058 -9.340490 -4.386639 30.1055932002-09-25 -10.216020 -9.480682 -3.933802 29.7585602002-09-26 -11.856774 -10.671012 -3.216025 29.369368[1000 rows x 4 columns]
Excel
读写MS Excel。
写:
In [145]: df.to_excel('foo.xlsx', sheet_name='Sheet1')
读:
In [146]: pd.read_excel('foo.xlsx', 'Sheet1', index_col=None, na_values=['NA'])Out[146]: A B C D2000-01-01 0.266457 -0.399641 -0.219582 1.1868602000-01-02 -1.170732 -0.345873 1.653061 -0.2829532000-01-03 -1.734933 0.530468 2.060811 -0.5155362000-01-04 -1.555121 1.452620 0.239859 -1.1568962000-01-05 0.578117 0.511371 0.103552 -2.4282022000-01-06 0.478344 0.449933 -0.741620 -1.9624092000-01-07 1.235339 -0.091757 -1.543861 -1.084753... ... ... ... ...2002-09-20 -10.628548 -9.153563 -7.883146 28.3139402002-09-21 -10.390377 -8.727491 -6.399645 30.9141072002-09-22 -8.985362 -8.485624 -4.669462 31.3677402002-09-23 -9.558560 -8.781216 -4.499815 30.5184392002-09-24 -9.902058 -9.340490 -4.386639 30.1055932002-09-25 -10.216020 -9.480682 -3.933802 29.7585602002-09-26 -11.856774 -10.671012 -3.216025 29.369368[1000 rows x 4 columns]
陷阱
>>> if pd.Series([False, True, False]): print("I was true")Traceback ...ValueError: The truth value of an array is ambiguous. Use a.empty, a.any() or a.all().
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