groupby

• Hiearchical index : index 2개인 경우
• reset_index() : index 새로 만들어 초기화
• sort_values
  -> hierarchical index일 때!
  
• df.describe(), df.describe().T

Case study

pivot table, crosstab

pivot table

crosstab

Merge & Concat

Merge

join

concat

• append : concat과 같은 효과
  
• axis 주의
• reset_index()

persistence

• Install
  • conda install openpyxl
  • conda install XlsxWriter

review

• groupby
• Hierarchical index
  • unstack()
  • swaplevel(), swaplevel.sortlevel(), swaplevel.sortvalues()
  • reset_index()
• grouped
  • get_group()
  • aggregation : 요약된 통계정보
  • transformation : 개별 데이터 변환
  • filter : 특정 조건(boolean) 검색
• .pivot_table()
• pd.crosstab()
• pd.merge(on=~), pd.merge(a,b,left_on=~, right_on)
• join
  • INNER JOIN
  • FULL JOIN
  • LEFT JOIN
  • RIGHT JOIN
    -> pd.merge(df_a, df_b, on=~, how=~)
  • index based : pd.merge(df_a, df_b, right_index=True, left_index=True)
• pd.concat(df_a, df_b, axis=~)
  • df_a.append(df_b)
• persistence
  • db connection
  • XLS persistence
  • Pickle persistence
    • .to_pickle()
    • .read_pickle()