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How to implement pivot() in pandas.DataFrame to convert rows to columns (code)

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2018-10-13 14:34:006350browse

The content of this article is about how pivot() in pandas.DataFrame implements row conversion (code). It has certain reference value. Friends in need can refer to it. I hope It will help you.

Example:

The following table needs to be converted between rows and columns:

The code is as follows:

# -*- coding:utf-8 -*-
import pandas as pd
import MySQLdb
from warnings import filterwarnings
# 由于create table if not exists总会抛出warning,因此使用filterwarnings消除
filterwarnings('ignore', category = MySQLdb.Warning)
from sqlalchemy import create_engine
import sys
if sys.version_info.major<3:
  reload(sys)
  sys.setdefaultencoding("utf-8")
  # 此脚本适用于python2和python3
host,port,user,passwd,db,charset="192.168.1.193",3306,"leo","mysql","test","utf8"

def get_df():
  global host,port,user,passwd,db,charset
  conn_config={"host":host, "port":port, "user":user, "passwd":passwd, "db":db,"charset":charset}
  conn = MySQLdb.connect(**conn_config)
  result_df=pd.read_sql(&#39;select UserName,Subject,Score from TEST&#39;,conn)
  return result_df

def pivot(result_df):
  df_pivoted_init=result_df.pivot(&#39;UserName&#39;,&#39;Subject&#39;,&#39;Score&#39;)
  df_pivoted = df_pivoted_init.reset_index()  # 将行索引也作为DataFrame值的一部分,以方便存储数据库
  return df_pivoted_init,df_pivoted
  # 返回的两个DataFrame,一个是以姓名作index的,一个是以数字序列作index,前者用于unpivot,后者用于save_to_mysql

def unpivot(df_pivoted_init):
  # unpivot需要进行df_pivoted_init二维表格的行、列索引遍历,需要拼SQL因此不能使用save_to_mysql存数据,这里使用SQL和MySQLdb接口存
  insert_sql="insert into test_unpivot(UserName,Subject,Score) values "
  # 处理值为NaN的情况
  df_pivoted_init=df_pivoted_init.add(0,fill_value=0)
  for col in df_pivoted_init.columns:
    for index in df_pivoted_init.index:
      value=df_pivoted_init.at[index,col]
      if value!=0:
        insert_sql=insert_sql+"(&#39;%s&#39;,&#39;%s&#39;,%s)" %(index,col,value)+&#39;,&#39;
  insert_sql = insert_sql.strip(&#39;,&#39;)
  global host, port, user, passwd, db, charset
  conn_config = {"host": host, "port": port, "user": user, "passwd": passwd, "db": db, "charset": charset}
  conn = MySQLdb.connect(**conn_config)
  cur=conn.cursor()
  cur.execute("create table if not exists test_unpivot like TEST")
  cur.execute(insert_sql)
  conn.commit()
  conn.close()

def save_to_mysql(df_pivoted,tablename):
  global host, port, user, passwd, db, charset
  """
  只有使用sqllite时才能指定con=connection实例,其他数据库需要使用sqlalchemy生成engine,engine的定义可以添加?来设置字符集和其他属性
  """
  conn="mysql://%s:%s@%s:%d/%s?charset=%s" %(user,passwd,host,port,db,charset)
  mysql_engine = create_engine(conn)
  df_pivoted.to_sql(name=tablename, con=mysql_engine, if_exists=&#39;replace&#39;, index=False)

# 从TEST表读取源数据至DataFrame结构
result_df=get_df()
# 将源数据行转列为二维表格形式
df_pivoted_init,df_pivoted=pivot(result_df)
# 将二维表格形式的数据存到新表test中
save_to_mysql(df_pivoted,&#39;test&#39;)
# 将被行转列的数据unpivot,存入test_unpivot表中
unpivot(df_pivoted_init)

The result is as follows:

About the pivot method that comes with the Pandas DataFrame class:

DataFrame.pivot(index=None, columns=None , values=None):

Return reshaped DataFrame organized by given index / column values.

There are only 3 parameters here because pivot The subsequent result must be a two-dimensional table, which only requires rows and columns and their corresponding values. And because it is a two-dimensional table, the is_pass column will definitely be lost after unpivot, so I did not check this column at the beginning.

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