pandas模块

Python从入门到放弃完整教程目录：https://www.cnblogs.com/nickchen121/p/10718112.html
pandas官方文档：[https://pandas.pydata.org/pandas-docs/stable/?v=20190307135750](https://pandas.pydata.org/pandas-docs/stable/?v=20190307135750)
pandas基于Numpy，可以看成是处理文本或者表格数据。pandas中有两个主要的数据结构，其中Series数据结构类似于Numpy中的一维数组，DataFrame类似于多维表格数据结构。

pandas是python数据分析的核心模块。它主要提供了五大功能:

支持文件存取操作，支持数据库(sql)、html、json、pickle、csv(txt、excel)、sas、stata、hdf等。
支持增删改查、切片、高阶函数、分组聚合等单表操作，以及和dict、list的互相转换。
支持多表拼接合并操作。
支持简单的绘图操作。
支持简单的统计分析操作。

一、Series数据结构

Series是一种类似于一维数组的对象，由一组数据和一组与之相关的数据标签（索引）组成。

Series比较像列表（数组）和字典的结合体

import numpy as np
import pandas as pd

df = pd.Series(0, index=['a', 'b', 'c', 'd'])
print(df)

a    0
b    0
c    0
d    0
dtype: int64

print(df.values)

[0 0 0 0]

print(df.index)

Index(['a', 'b', 'c', 'd'], dtype='object')

1.1 Series支持NumPy模块的特性（下标）

详解	方法
从ndarray创建Series	Series(arr)
与标量运算	df*2
两个Series运算	df1+df2
索引	df[0], df[[1,2,4]]
切片	df[0:2]
通用函数	np.abs(df)
布尔值过滤	df[df>0]

arr = np.array([1, 2, 3, 4, np.nan])
print(arr)

[ 1.  2.  3.  4. nan]

df = pd.Series(arr, index=['a', 'b', 'c', 'd', 'e'])
print(df)

a    1.0
b    2.0
c    3.0
d    4.0
e    NaN
dtype: float64

print(df**2)

a     1.0
b     4.0
c     9.0
d    16.0
e     NaN
dtype: float64

print(df[0])

1.0

print(df['a'])

1.0

print(df[[0, 1, 2]])

a    1.0
b    2.0
c    3.0
dtype: float64

print(df[0:2])

a    1.0
b    2.0
dtype: float64

np.sin(df)

a    0.841471
b    0.909297
c    0.141120
d   -0.756802
e         NaN
dtype: float64

df[df > 1]

b    2.0
c    3.0
d    4.0
dtype: float64

1.2 Series支持字典的特性（标签）

详解	方法
从字典创建Series	Series(dic),
in运算	’a’ in sr
键索引	sr['a'], sr[['a', 'b', 'd']]

df = pd.Series({'a': 1, 'b': 2})
print(df)

a    1
b    2
dtype: int64

print('a' in df)

True

print(df['a'])

1.3 Series缺失数据处理

方法	详解
dropna()	过滤掉值为NaN的行
fillna()	填充缺失数据
isnull()	返回布尔数组，缺失值对应为True
notnull()	返回布尔数组，缺失值对应为False

df = pd.Series([1, 2, 3, 4, np.nan], index=['a', 'b', 'c', 'd', 'e'])
print(df)

a    1.0
b    2.0
c    3.0
d    4.0
e    NaN
dtype: float64

print(df.dropna())

a    1.0
b    2.0
c    3.0
d    4.0
dtype: float64

print(df.fillna(5))

a    1.0
b    2.0
c    3.0
d    4.0
e    5.0
dtype: float64

print(df.isnull())

a    False
b    False
c    False
d    False
e     True
dtype: bool

print(df.notnull())

a     True
b     True
c     True
d     True
e    False
dtype: bool

二、DataFrame数据结构

DataFrame是一个表格型的数据结构，含有一组有序的列。

DataFrame可以被看做是由Series组成的字典，并且共用一个索引。

2.1 产生时间对象数组：date_range

date_range参数详解：

参数	详解
start	开始时间
end	结束时间
periods	时间长度
freq	时间频率，默认为'D'，可选H(our),W(eek),B(usiness),S(emi-)M(onth),(min)T(es), S(econd), A(year),…

dates = pd.date_range('20190101', periods=6, freq='M')
print(dates)

DatetimeIndex(['2019-01-31', '2019-02-28', '2019-03-31', '2019-04-30',
               '2019-05-31', '2019-06-30'],
              dtype='datetime64[ns]', freq='M')

np.random.seed(1)
arr = 10 * np.random.randn(6, 4)
print(arr)

[[ 16.24345364  -6.11756414  -5.28171752 -10.72968622]
 [  8.65407629 -23.01538697  17.44811764  -7.61206901]
 [  3.19039096  -2.49370375  14.62107937 -20.60140709]
 [ -3.22417204  -3.84054355  11.33769442 -10.99891267]
 [ -1.72428208  -8.77858418   0.42213747   5.82815214]
 [-11.00619177  11.4472371    9.01590721   5.02494339]]

df = pd.DataFrame(arr, index=dates, columns=['c1', 'c2', 'c3', 'c4'])
df

	c1	c2	c3
16.243454	-6.117564	-5.281718	-10.729686
8.654076	-23.015387	17.448118	-7.612069
3.190391	-2.493704	14.621079	-20.601407
-3.224172	-3.840544	11.337694	-10.998913
-1.724282	-8.778584	0.422137	5.828152
-11.006192	11.447237	9.015907	5.024943

三、DataFrame属性

属性	详解
dtype是	查看数据类型
index	查看行序列或者索引
columns	查看各列的标签
values	查看数据框内的数据，也即不含表头索引的数据
describe	查看数据每一列的极值，均值，中位数，只可用于数值型数据
transpose	转置，也可用Ｔ来操作
sort_index	排序，可按行或列index排序输出
sort_values	按数据值来排序

# 查看数据类型
print(df2.dtypes)

0    float64
1    float64
2    float64
3    float64
dtype: object

df

	c1	c2	c3
16.243454	-6.117564	-5.281718	-10.729686
8.654076	-23.015387	17.448118	-7.612069
3.190391	-2.493704	14.621079	-20.601407
-3.224172	-3.840544	11.337694	-10.998913
-1.724282	-8.778584	0.422137	5.828152
-11.006192	11.447237	9.015907	5.024943

print(df.index)

DatetimeIndex(['2019-01-31', '2019-02-28', '2019-03-31', '2019-04-30',
               '2019-05-31', '2019-06-30'],
              dtype='datetime64[ns]', freq='M')

print(df.columns)

Index(['c1', 'c2', 'c3', 'c4'], dtype='object')

print(df.values)

[[ 16.24345364  -6.11756414  -5.28171752 -10.72968622]
 [  8.65407629 -23.01538697  17.44811764  -7.61206901]
 [  3.19039096  -2.49370375  14.62107937 -20.60140709]
 [ -3.22417204  -3.84054355  11.33769442 -10.99891267]
 [ -1.72428208  -8.77858418   0.42213747   5.82815214]
 [-11.00619177  11.4472371    9.01590721   5.02494339]]

df.describe()

	c1	c2	c3
6.000000	6.000000	6.000000	6.000000
2.022213	-5.466424	7.927203	-6.514830
9.580084	11.107772	8.707171	10.227641
-11.006192	-23.015387	-5.281718	-20.601407
-2.849200	-8.113329	2.570580	-10.931606
0.733054	-4.979054	10.176801	-9.170878
7.288155	-2.830414	13.800233	1.865690
16.243454	11.447237	17.448118	5.828152

df.T

	2019-01-31 00:00:00	2019-02-28 00:00:00	2019-03-31 00:00:00	2019-04-30 00:00:00	2019-05-31 00:00:00
16.243454	8.654076	3.190391	-3.224172	-1.724282	-11.006192
-6.117564	-23.015387	-2.493704	-3.840544	-8.778584	11.447237
-5.281718	17.448118	14.621079	11.337694	0.422137	9.015907
-10.729686	-7.612069	-20.601407	-10.998913	5.828152	5.024943

# 按行标签[c1, c2, c3, c4]从大到小排序
df.sort_index(axis=0)

	c1	c2	c3
16.243454	-6.117564	-5.281718	-10.729686
8.654076	-23.015387	17.448118	-7.612069
3.190391	-2.493704	14.621079	-20.601407
-3.224172	-3.840544	11.337694	-10.998913
-1.724282	-8.778584	0.422137	5.828152
-11.006192	11.447237	9.015907	5.024943

# 按列标签[2019-01-01, 2019-01-02...]从大到小排序
df.sort_index(axis=1)

	c1	c2	c3
16.243454	-6.117564	-5.281718	-10.729686
8.654076	-23.015387	17.448118	-7.612069
3.190391	-2.493704	14.621079	-20.601407
-3.224172	-3.840544	11.337694	-10.998913
-1.724282	-8.778584	0.422137	5.828152
-11.006192	11.447237	9.015907	5.024943

# 按c2列的值从大到小排序
df.sort_values(by='c2')

	c1	c2	c3
8.654076	-23.015387	17.448118	-7.612069
-1.724282	-8.778584	0.422137	5.828152
16.243454	-6.117564	-5.281718	-10.729686
-3.224172	-3.840544	11.337694	-10.998913
3.190391	-2.493704	14.621079	-20.601407
-11.006192	11.447237	9.015907	5.024943

四、DataFrame取值

df

	c1	c2	c3
16.243454	-6.117564	-5.281718	-10.729686
8.654076	-23.015387	17.448118	-7.612069
3.190391	-2.493704	14.621079	-20.601407
-3.224172	-3.840544	11.337694	-10.998913
-1.724282	-8.778584	0.422137	5.828152
-11.006192	11.447237	9.015907	5.024943

4.1 通过columns取值

df['c2']

2019-01-31    -6.117564
2019-02-28   -23.015387
2019-03-31    -2.493704
2019-04-30    -3.840544
2019-05-31    -8.778584
2019-06-30    11.447237
Freq: M, Name: c2, dtype: float64

df[['c2', 'c3']]

	c2	c3
-6.117564	-5.281718
-23.015387	17.448118
-2.493704	14.621079
-3.840544	11.337694
-8.778584	0.422137
11.447237	9.015907

4.2 loc（通过行标签取值）

# 通过自定义的行标签选择数据
df.loc['2019-01-01':'2019-01-03']

	c1	c2	c3	c4

df[0:3]

	c1	c2	c3
16.243454	-6.117564	-5.281718	-10.729686
8.654076	-23.015387	17.448118	-7.612069
3.190391	-2.493704	14.621079	-20.601407

4.3 iloc（类似于numpy数组取值）

df.values

array([[ 16.24345364,  -6.11756414,  -5.28171752, -10.72968622],
       [  8.65407629, -23.01538697,  17.44811764,  -7.61206901],
       [  3.19039096,  -2.49370375,  14.62107937, -20.60140709],
       [ -3.22417204,  -3.84054355,  11.33769442, -10.99891267],
       [ -1.72428208,  -8.77858418,   0.42213747,   5.82815214],
       [-11.00619177,  11.4472371 ,   9.01590721,   5.02494339]])

# 通过行索引选择数据
print(df.iloc[2, 1])

-2.493703754774101

df.iloc[1:4, 1:4]

	c2	c3
-23.015387	17.448118	-7.612069
-2.493704	14.621079	-20.601407
-3.840544	11.337694	-10.998913

4.4 使用逻辑判断取值

df[df['c1'] > 0]

	c1	c2	c3
16.243454	-6.117564	-5.281718	-10.729686
8.654076	-23.015387	17.448118	-7.612069
3.190391	-2.493704	14.621079	-20.601407

df[(df['c1'] > 0) & (df['c2'] > -8)]

	c1	c2	c3	c4
16.243454	-6.117564	-5.281718	-10.729686
3.190391	-2.493704	14.621079	-20.601407

五、DataFrame值替换

df

	c1	c2	c3
16.243454	-6.117564	-5.281718	-10.729686
8.654076	-23.015387	17.448118	-7.612069
3.190391	-2.493704	14.621079	-20.601407
-3.224172	-3.840544	11.337694	-10.998913
-1.724282	-8.778584	0.422137	5.828152
-11.006192	11.447237	9.015907	5.024943

df.iloc[0:3, 0:2] = 0
df

	c1	c2	c3
0.000000	0.000000	-5.281718	-10.729686
0.000000	0.000000	17.448118	-7.612069
0.000000	0.000000	14.621079	-20.601407
-3.224172	-3.840544	11.337694	-10.998913
-1.724282	-8.778584	0.422137	5.828152
-11.006192	11.447237	9.015907	5.024943

df['c3'] > 10

2019-01-31    False
2019-02-28     True
2019-03-31     True
2019-04-30     True
2019-05-31    False
2019-06-30    False
Freq: M, Name: c3, dtype: bool

# 针对行做处理
df[df['c3'] > 10] = 100
df

	c1	c2	c3
0.000000	0.000000	-5.281718	-10.729686
100.000000	100.000000	100.000000	100.000000
100.000000	100.000000	100.000000	100.000000
100.000000	100.000000	100.000000	100.000000
-1.724282	-8.778584	0.422137	5.828152
-11.006192	11.447237	9.015907	5.024943

# 针对行做处理
df = df.astype(np.int32)
df[df['c3'].isin([100])] = 1000
df

	c1	c2	c3
0	0	-5	-10
1000	1000	1000	1000
1000	1000	1000	1000
1000	1000	1000	1000
-1	-8	0	5
-11	11	9	5

六、读取CSV文件

import pandas as pd
from io import StringIO
test_data = '''
5.1,,1.4,0.2
4.9,3.0,1.4,0.2
4.7,3.2,,0.2
7.0,3.2,4.7,1.4
6.4,3.2,4.5,1.5
6.9,3.1,4.9,
,,,
'''

test_data = StringIO(test_data)
df = pd.read_csv(test_data, header=None)
df.columns = ['c1', 'c2', 'c3', 'c4']
df

	c1	c2	c3
5.1	NaN	1.4	0.2
4.9	3.0	1.4	0.2
4.7	3.2	NaN	0.2
7.0	3.2	4.7	1.4
6.4	3.2	4.5	1.5
6.9	3.1	4.9	NaN
NaN	NaN	NaN	NaN

七、处理丢失数据

df.isnull()

	c1	c2	c3
False	True	False	False
False	False	False	False
False	False	True	False
False	False	False	False
False	False	False	False
False	False	False	True
True	True	True	True

# 通过在isnull()方法后使用sum()方法即可获得该数据集某个特征含有多少个缺失值
print(df.isnull().sum())

c1    1
c2    2
c3    2
c4    2
dtype: int64

# axis=0删除有NaN值的行
df.dropna(axis=0)

	c1	c2	c3
4.9	3.0	1.4	0.2
7.0	3.2	4.7	1.4
6.4	3.2	4.5	1.5

# axis=1删除有NaN值的列
df.dropna(axis=1)

# 删除全为NaN值得行或列
df.dropna(how='all')

	c1	c2	c3
5.1	NaN	1.4	0.2
4.9	3.0	1.4	0.2
4.7	3.2	NaN	0.2
7.0	3.2	4.7	1.4
6.4	3.2	4.5	1.5
6.9	3.1	4.9	NaN

# 删除行不为4个值的
df.dropna(thresh=4)

	c1	c2	c3
4.9	3.0	1.4	0.2
7.0	3.2	4.7	1.4
6.4	3.2	4.5	1.5

# 删除c2中有NaN值的行
df.dropna(subset=['c2'])

	c1	c2	c3
4.9	3.0	1.4	0.2
4.7	3.2	NaN	0.2
7.0	3.2	4.7	1.4
6.4	3.2	4.5	1.5
6.9	3.1	4.9	NaN

# 填充nan值
df.fillna(value=10)

	c1	c2	c3
5.1	10.0	1.4	0.2
4.9	3.0	1.4	0.2
4.7	3.2	10.0	0.2
7.0	3.2	4.7	1.4
6.4	3.2	4.5	1.5
6.9	3.1	4.9	10.0
10.0	10.0	10.0	10.0

八、合并数据

df1 = pd.DataFrame(np.zeros((3, 4)))
df1

	0	1	2	3
0.0	0.0	0.0	0.0
0.0	0.0	0.0	0.0
0.0	0.0	0.0	0.0

df2 = pd.DataFrame(np.ones((3, 4)))
df2

	0	1	2
1.0	1.0	1.0	1.0
1.0	1.0	1.0	1.0
1.0	1.0	1.0	1.0

# axis=0合并列
pd.concat((df1, df2), axis=0)

	0	1	2
0.0	0.0	0.0	0.0
0.0	0.0	0.0	0.0
0.0	0.0	0.0	0.0
1.0	1.0	1.0	1.0
1.0	1.0	1.0	1.0
1.0	1.0	1.0	1.0

# axis=1合并行
pd.concat((df1, df2), axis=1)

3	0	1	2
1.0	1.0	1.0	1.0
1.0	1.0	1.0	1.0
1.0	1.0	1.0	1.0

# append只能合并列
df1.append(df2)

	0	1	2
0.0	0.0	0.0	0.0
0.0	0.0	0.0	0.0
0.0	0.0	0.0	0.0
1.0	1.0	1.0	1.0
1.0	1.0	1.0	1.0
1.0	1.0	1.0	1.0

九、导入导出数据

使用df = pd.read_excel(filename)读取文件，使用df.to_excel(filename)保存文件。

9.1 读取文件导入数据

读取文件导入数据函数主要参数：

参数	详解
sep	指定分隔符，可用正则表达式如'\s+'
header=None	指定文件无行名
name	指定列名
index_col	指定某列作为索引
skip_row	指定跳过某些行
na_values	指定某些字符串表示缺失值
parse_dates	指定某些列是否被解析为日期，布尔值或列表

df = pd.read_excel(filename)
df = pd.read_csv(filename)

9.2 写入文件导出数据

写入文件函数的主要参数：

参数	详解
sep	分隔符
na_rep	指定缺失值转换的字符串，默认为空字符串
header=False	不保存列名
index=False	不保存行索引
cols	指定输出的列，传入列表

df.to_excel(filename)

十、pandas读取json文件

strtext = '[{"ttery":"min","issue":"20130801-3391","code":"8,4,5,2,9","code1":"297734529","code2":null,"time":1013395466000},\
{"ttery":"min","issue":"20130801-3390","code":"7,8,2,1,2","code1":"298058212","code2":null,"time":1013395406000},\
{"ttery":"min","issue":"20130801-3389","code":"5,9,1,2,9","code1":"298329129","code2":null,"time":1013395346000},\
{"ttery":"min","issue":"20130801-3388","code":"3,8,7,3,3","code1":"298588733","code2":null,"time":1013395286000},\
{"ttery":"min","issue":"20130801-3387","code":"0,8,5,2,7","code1":"298818527","code2":null,"time":1013395226000}]'

df = pd.read_json(strtext, orient='records')
df

	code	code1	code2	issue	time
8,4,5,2,9	297734529	NaN	20130801-3391	1013395466000	min
7,8,2,1,2	298058212	NaN	20130801-3390	1013395406000	min
5,9,1,2,9	298329129	NaN	20130801-3389	1013395346000	min
3,8,7,3,3	298588733	NaN	20130801-3388	1013395286000	min
0,8,5,2,7	298818527	NaN	20130801-3387	1013395226000	min

df.to_excel('pandas处理json.xlsx',
            index=False,
            columns=["ttery", "issue", "code", "code1", "code2", "time"])

10.1 orient参数的五种形式

orient是表明预期的json字符串格式。orient的设置有以下五个值：

1.'split' : dict like {index -> [index], columns -> [columns], data -> [values]}

这种就是有索引，有列字段,和数据矩阵构成的json格式。key名称只能是index,columns和data。

s = '{"index":[1,2,3],"columns":["a","b"],"data":[[1,3],[2,8],[3,9]]}'
df = pd.read_json(s, orient='split')
df

	a	b
1	3
2	8
3	9

2.'records' : list like [{column -> value}, ... , {column -> value}]

这种就是成员为字典的列表。如我今天要处理的json数据示例所见。构成是列字段为键,值为键值,每一个字典成员就构成了dataframe的一行数据。

strtext = '[{"ttery":"min","issue":"20130801-3391","code":"8,4,5,2,9","code1":"297734529","code2":null,"time":1013395466000},\
{"ttery":"min","issue":"20130801-3390","code":"7,8,2,1,2","code1":"298058212","code2":null,"time":1013395406000}]'

df = pd.read_json(strtext, orient='records')
df

	code	code1	code2	issue	time	ttery
8,4,5,2,9	297734529	NaN	20130801-3391	1013395466000	min
7,8,2,1,2	298058212	NaN	20130801-3390	1013395406000	min

3.'index' : dict like {index -> {column -> value}}

以索引为key,以列字段构成的字典为键值。如：

s = '{"0":{"a":1,"b":2},"1":{"a":9,"b":11}}'
df = pd.read_json(s, orient='index')
df

	a	b
1	2
9	11

4.'columns' : dict like {column -> {index -> value}}

这种处理的就是以列为键，对应一个值字典的对象。这个字典对象以索引为键,以值为键值构成的json字符串。如下图所示:

s = '{"a":{"0":1,"1":9},"b":{"0":2,"1":11}}'
df = pd.read_json(s, orient='columns')
df

	a	b
1	2
9	11

5.'values' : just the values array。

values这种我们就很常见了。就是一个嵌套的列表。里面的成员也是列表，2层的。

s = '[["a",1],["b",2]]'
df = pd.read_json(s, orient='values')
df

	0	1
a	1
b	2

十一、pandas读取sql语句

import numpy as np
import pandas as pd
import pymysql


def conn(sql):
    # 连接到mysql数据库
    conn = pymysql.connect(
        host="localhost",
        port=3306,
        user="root",
        passwd="123",
        db="db1",
    )
    try:
        data = pd.read_sql(sql, con=conn)
        return data
    except Exception as e:
        print("SQL is not correct!")
    finally:
        conn.close()


sql = "select * from test1 limit 0, 10"  # sql语句
data = conn(sql)
print(data.columns.tolist())  # 查看字段
print(data)  # 查看数据

posted @ 2019-05-04 09:39 B站-水论文的程序猿阅读(3257) 评论(1) 编辑收藏举报

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