python pandas学习笔记

reshape

• 描述：

   更改dataframe的数据维度

• 备注：

   -1 代表指定后剩余的

   numpy和dataframe使用方法类似

• 示例：

import numpy as np
array = np.array(np.arange(12))
print('shape of array:\n', array.shape)
array_reshape = array.reshape(3,4)
print('shape of array_reshape: \n', array_reshape.shape)

array_reshape_1 = array.reshape(4,-1)
print('shape of array_shape_1:\n', array_reshape_1.shape)

shape of array:
 (12,)
shape of array_reshape:
 (3, 4)
shape of array_shape_1:
 (4, 3)

pandas.Index, columns, set_names

• 描述：

   index:指定行索引

   columns:指定列索引，并指定行索引列名

• 参考链接：

https://pandas.pydata.org/pandas-docs/stable/generated/pandas.Index.html

http://pandas.pydata.org/pandas-docs/stable/generated/pandas.Index.set_names.html

• 示例：

import pandas as pd
b = np.array(np.arange(12)).reshape(3,4)
df = pd.DataFrame(b, index = ['A','B','C'],
             columns = pd.Index(['a','b','c','d']
                                ,name = 'index_name'))
print('df:\n',df)

df.columns = ['a_r','b_r','c_r','d_r']
print('columns after rename :\n',df.columns)

df.index.set_names('index_rename', inplace = True)
print('rename index name :\n', df)

df:
 index_name  a  b   c   d
A           0  1   2   3
B           4  5   6   7
C           8  9  10  11
columns after rename :
 Index(['a_r', 'b_r', 'c_r', 'd_r'], dtype='object')
rename index name :
               a_r  b_r  c_r  d_r
index_rename
A               0    1    2    3
B               4    5    6    7
C               8    9   10   11

python2 pandas连接mysql

import MySQLdb
conn=MySQLdb.connect(host= host, user = username, passwd=password,
                    port = port, db = db, charset='utf-8')
df = pd.read_sql(sql, conn, index_col="id")