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Python: 如何用 pandas.DataFrame.groupby 做樞紐分析? DataFrame.groupby (by=None, axis=0, level=None, as_index=True, sort=True, group_keys=True, observed=False, dropna=True) ; 如何將資料夾中的多個csv檔求平均?

DataFrame.groupby(by=None, axis=0, level=None, 
as_index=True, sort=True, group_keys=True, 
observed=False, dropna=True)

點此或下圖連結官網:

實用的, by=label or list of labels
A label or list of labels may be passed to group by the columns in self.

實用的, level=0
(通常只有一層index,
依據第0層的index做分類)

官網範例:

df.groupby([‘Animal’]).mean()
#’Animal’為index

df.groupby([‘Animal’],as_index=False).mean()

#’Animal’ 變為columns,而非index

df.groupby([‘Animal’]).mean().reset_index()

#跟as_index=False同效果,
#把 ‘Animal’ 從index重新推回columns
#as_index=False 也有機會用到,
#但使用 reset_index() 更熟悉

Hierarchical Indexes #多層index

df.groupby(level=0).mean()

如果資料夾中有兩個屬於資料的csv,
以及其他非資料非csv的檔案,
如何將兩個csv的資料做平均?

code:

import pandas as pd
import numpy as np
import glob 
from typing import List
import os

folder = r"C:\Python\z correction\X Cut"
#X Cut , Y Cut資料夾需要分開
fname  = "*.csv"
cut = "X" # Y

def folder_fname2lis_fpath(folder,fname="*.csv"):
    fpath  = "\\".join([folder,fname]) 
    lis_fpath = glob.glob(fpath)
    return lis_fpath

lis_fpath:List[str] = folder_fname2lis_fpath(folder,fname="*.csv")
# ['C:\\Python\\z correction\\X Cut\\X cut 1st_-11cm to 11cm.csv',
#  'C:\\Python\\z correction\\X Cut\\X cut 2nd_-11cm to 11cm.csv']

def lis_fpath2lisDF(lis_fpath:List[str]):
    lisDF:List[pd.DataFrame] = []
    for fpath in lis_fpath:
        df = pd.read_csv(fpath)
        df = df[["X","Y","Z"]]
        # [111 rows x 3 columns]
        lisDF.append(df)
        
    return lisDF #不要誤入for迴圈的縮排中

lisDF:List[pd.DataFrame] = lis_fpath2lisDF(lis_fpath)
#lisDF 中的兩個DF,都是[111 rows x 3 columns],
#index都是0~110一致的 
#重要,需確定index都一樣,後面的groupby()才不會做錯

def lisDF2avg_df(lisDF:List[pd.DataFrame]):
    if len(lisDF) >= 2:
        # 计算平均值
        avg_df = pd.concat(lisDF).groupby(level=0).mean()
    else:
        avg_df = lisDF[0]   
    return avg_df

avg_df:pd.DataFrame = lisDF2avg_df(lisDF)
#[111 rows x 3 columns]  正確
currentFolder = os.getcwd()
#'C:\\Python\\z correction'
exFolder = "\\".join([currentFolder,"export"])
#'C:\\Python\\z correction\\export'
if not os.path.exists(exFolder):
    os.makedirs(exFolder)
xlsx_path = "\\".join([exFolder,f"avg_df for {cut} Cut.xlsx"])
#'C:\\Python\\z correction\\export\\avg_df for X Cut.xlsx'
avg_df.to_excel(xlsx_path)
print(f"xlsx檔案已經輸出到:\n{xlsx_path}\n")
#C:\Python\z correction\X Cut\X Cut Avg.ods #手工算Avg
#跟手工算的Avg 比對無誤