0-2 pandas 复习

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1-1 初识pandas

创建序列

s = pd.Series([1, 3, 6, np.nan, 44, 1])
print(s)
"""
            0     1.0
            1     3.0
            2     6.0
            3     NaN
            4    44.0
            5     1.0
            dtype: float64
"""

创建日期型数据，并增长六个日期

date = pd.date_range('2016-01-01', periods = 6)
print(date)
"""
DatetimeIndex(['2016-01-01', '2016-01-02', '2016-01-03', '2016-01-04',
               '2016-01-05', '2016-01-06'],
              dtype='datetime64[ns]', freq='D')
"""

创建有索引和字符串的数据

df = pd.DataFrame(np.random.rand(6,4), index=date, columns=['a', 'b', 'c', 'd'])
print(df)
"""
                   a         b         c         d
2016-01-01  0.113951  0.583000  0.167336  0.917897
2016-01-02  0.632843  0.950597  0.280311  0.946806
2016-01-03  0.367501  0.313236  0.475095  0.889570
2016-01-04  0.653676  0.444720  0.091550  0.272699
2016-01-05  0.448919  0.328602  0.644945  0.196358
2016-01-06  0.656723  0.355628  0.886951  0.688788
"""

不加索引的矩阵

df1 = pd.DataFrame(np.arange(12).reshape((3,4)))
print(df1)

# 创建决定各个数值的矩阵 categorical 明确的，确定的
df2 = pd.DataFrame({'A':1,
                    'B':pd.Timestamp('20120202'),
                    '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'
                    })
print(df2)
"""
   A          B    C  D      E    F
0  1 2012-02-02  1.0  3   test  foo
1  1 2012-02-02  1.0  3  train  foo
2  1 2012-02-02  1.0  3   test  foo
3  1 2012-02-02  1.0  3  train  foo
"""
# df2 的dtype
print(df2.dtypes)
"""
A             int64
B    datetime64[ns]
C           float32
D             int32
E          category
F            object
dtype: object
"""
# 列标
print(df2.columns)
"Index(['A', 'B', 'C', 'D', 'E', 'F'], dtype='object')"
# 值
print(df2.values)
"""
[[1 Timestamp('2012-02-02 00:00:00') 1.0 3 'test' 'foo']
 [1 Timestamp('2012-02-02 00:00:00') 1.0 3 'train' 'foo']
 [1 Timestamp('2012-02-02 00:00:00') 1.0 3 'test' 'foo']
 [1 Timestamp('2012-02-02 00:00:00') 1.0 3 'train' 'foo']]
"""
# 描述
print(df2.describe())
"""
         A    C    D
count  4.0  4.0  4.0
mean   1.0  1.0  3.0
std    0.0  0.0  0.0
min    1.0  1.0  3.0
25%    1.0  1.0  3.0
50%    1.0  1.0  3.0
75%    1.0  1.0  3.0
max    1.0  1.0  3.0
"""
# 转置
print(df2.T)
# 按列或者行排序
print(df2.sort_index(axis=1, ascending=False))
"""
     F      E  D    C          B  A
0  foo   test  3  1.0 2012-02-02  1
1  foo  train  3  1.0 2012-02-02  1
2  foo   test  3  1.0 2012-02-02  1
3  foo  train  3  1.0 2012-02-02  1
"""
# 输出部分索引的值并排序
print(df2.sort_values(by='E'))
"""
   A          B    C  D      E    F
0  1 2012-02-02  1.0  3   test  foo
2  1 2012-02-02  1.0  3   test  foo
1  1 2012-02-02  1.0  3  train  foo
3  1 2012-02-02  1.0  3  train  foonn 
"""

1-2 数据处理

# 先创建数据备用
date = pd.date_range('20130101', periods=6)
df = pd.DataFrame(np.arange(24).reshape((6,4)), index=date, columns=['A', 'B', 'C', 'D'])
print(df)
# 多种方式打印
print(df['A'])
print(df.A)
# 打印前三行
print(df[0:3])
# print('\n'*1)
# 打印后三行
print(df['2013-01-04':'2013-01-06'])
# select by label:loc
print(df.loc['2013-01-06'])
"""
A    20
B    21
C    22
D    23
Name: 2013-01-06 00:00:00, dtype: int32
"""
print(df.loc[:,['A', 'B']])
"""
             A   B
2013-01-01   0   1
2013-01-02   4   5
2013-01-03   8   9
2013-01-04  12  13
2013-01-05  16  17
2013-01-06  20  21
"""
print(df.loc['2013-01-03', ['A', 'B']])
"""
A    8
B    9
Name: 2013-01-03 00:00:00, dtype: int32
"""

# select by of position：iloc
print(df.iloc[[1, 3, 5], 1:3])
"""
             B   C
2013-01-02   5   6
2013-01-04  13  14
2013-01-06  21  22
"""
# select mixed: ix
# print(df.ix[:3, ['A', 'B', 'C']])

# boolean indexing
print(df)
print(df<8)
print(df[df.A<8])
"""
                A      B      C      D
2013-01-01   True   True   True   True
2013-01-02   True   True   True   True
2013-01-03  False  False  False  False
2013-01-04  False  False  False  False
2013-01-05  False  False  False  False
2013-01-06  False  False  False  False

            A  B  C  D
2013-01-01  0  1  2  3
2013-01-02  4  5  6  7

"""

1-3 设置数据值

date = pd.date_range('20100101', periods=6)
df = pd.DataFrame(np.arange(24).reshape((6, 4)), index=date, columns=['A', 'B', 'C', 'D'])
print(df)

# set values by position: iloc
df.iloc[2,2] = 111
print(df)
# set values by label: loc
df.loc['20100103', 'B'] = 999
print(df)
# 设置>大于某个数的值  改变全部值
# df[df.A>0] = 0
# print(df)
"""
            A  B  C  D
2010-01-01  0  1  2  3
2010-01-02  0  0  0  0
2010-01-03  0  0  0  0
2010-01-04  0  0  0  0
2010-01-05  0  0  0  0
2010-01-06  0  0  0  0
"""
# 改变一部分的值
# df.A[df.A>3] = 0
# print(df)
"""
            A    B    C   D
2010-01-01  0    1    2   3
2010-01-02  0    5    6   7
2010-01-03  0  999  111  11
2010-01-04  0   13   14  15
2010-01-05  0   17   18  19
2010-01-06  0   21   22  23
"""
# 增加值
df['F'] = np.nan
print(df)
"""
             A    B    C   D   F
2010-01-01   0    1    2   3 NaN
2010-01-02   4    5    6   7 NaN
2010-01-03   8  999  111  11 NaN
2010-01-04  12   13   14  15 NaN
2010-01-05  16   17   18  19 NaN
2010-01-06  20   21   22  23 NaN
"""
df['E'] = pd.Series([1,2,3,4,5,6], index=pd.date_range('20100101', periods=6))
print(df)
             A    B    C   D   F  E
2010-01-01   0    1    2   3 NaN  1
2010-01-02   4    5    6   7 NaN  2
2010-01-03   8  999  111  11 NaN  3
2010-01-04  12   13   14  15 NaN  4
2010-01-05  16   17   18  19 NaN  5
2010-01-06  20   21   22  23 NaN  6

1-4 处理丢失的数据

import numpy as np
import pandas as pd

# 原始数据
date = pd.date_range('20100101', periods=6)
df = pd.DataFrame(np.arange(24).reshape((6, 4)), index=date, columns=['A', 'B', 'C', 'D'])
print(df)
df.iloc[0, 1] = np.nan
df.iloc[1, 2] = np.nan
print(df)
# 处理数据-丢掉有nan的整行数据  any-只要行或列中年有nan就算，all-要全部都为nan才算
print(df.dropna(axis=0, how='any'))   # axis = 0， 竖直方向对行进行操作
print(df.dropna(axis=1, how='any'))   # axis = 1   水平方向对列进行操作
"""
             A     B     C   D
2010-01-03   8   9.0  10.0  11
2010-01-04  12  13.0  14.0  15
2010-01-05  16  17.0  18.0  19
2010-01-06  20  21.0  22.0  23
          A   D
2010-01-01   0   3
2010-01-02   4   7
2010-01-03   8  11
2010-01-04  12  15
2010-01-05  16  19
2010-01-06  20  23
"""
# 将nan的位置填入其他值，如0
print(df.fillna(value=0))
"""
             A     B     C   D
2010-01-01   0   0.0   2.0   3
2010-01-02   4   5.0   0.0   7
2010-01-03   8   9.0  10.0  11
2010-01-04  12  13.0  14.0  15
2010-01-05  16  17.0  18.0  19
2010-01-06  20  21.0  22.0  23
"""
# 打印True或者False的值
print(df.isnull())
"""
                A      B      C      D
2010-01-01  False   True  False  False
2010-01-02  False  False   True  False
2010-01-03  False  False  False  False
2010-01-04  False  False  False  False
2010-01-05  False  False  False  False
2010-01-06  False  False  False  False
"""
# 打印至少一个是丢失的数据的判断情况
print(np.any(df.isnull()))   # True

1-5 导入与导出数据

# 将csv文件读入，该文件可以再=在任意目录，将其读入就可以
data = pd.read_csv('C:/Users/liyuelong/Desktop/student.csv')
print(data)
# 转成其他模式，目录地址要相同。
data.to_pickle('C:/Users/liyuelong/Desktop/student.pickle')

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