[英]Best way to sort txt file using csv tools in python
我有以下代碼,並試圖以最簡單的方法對文件內容進行排序。
import csv
import operator
#==========Search by ID number. Return Just the Name Fields for the Student
with open("studentinfo.txt","r") as f:
studentfileReader=csv.reader(f)
id=input("Enter Id:")
for row in studentfileReader:
for field in row:
if field==id:
currentindex=row.index(id)
print(row[currentindex+1]+" "+row[currentindex+2])
#=========Sort by Last Name
with open("studentinfo.txt","r") as f:
studentfileReader=csv.reader(f)
sortedlist=sorted(f,key=operator.itemgetter(0),reverse=True)
print(sortedlist)
我知道各種可能的解決方案,但不能完全使它們正常運行,並且出於教學/學習的目的,我會對最簡單有效的解決方案感興趣, 並給出了明確的解釋。
研究包括: ****導入運算符**** sortedlist = sorted(閱讀器,鍵= operator.itemgetter(3),reverse = True)
或使用lambda sortedlist = sorted(閱讀器,鍵= lambda行:row [3],reverse = True)
對於ANSWER,如果有人可以發布完整的解決方案,並按姓氏和ID號進行排序,以說明兩個不同的示例,我將不勝感激。 答案的擴展將是在此特定示例中顯示如何按多個值排序:
完整代碼清單:
文件內容
002,Ash,Smith,Test1:20,Test2:20,Test3:100003
004,Grace,Asha,Test1:33,Test2:54,Test3:23
005,Cat,Zelch,Test1:66,Test2:22,Test3:11
001,Joe,Bloggs,Test1:99,Test2:100,Test3:1
003,Jonathan,Peter,Test1:99,Test2:33,Test3:44
您可以使用lambda
函數按csv
閱讀器返回的列表的任何鍵進行排序,例如,按姓氏(第三列)進行排序:
with open("studentinfo.txt", "r") as f:
reader = csv.reader(f)
sorted_list = list(reader) # turn the reader iterator into a list
sorted_list.sort(key=lambda x: x[2]) # use the third column as a sorting key
print("\n".join(str(row) for row in sorted_list)) # prettier print
或按ID(第一列):
with open("studentinfo.txt", "r") as f:
reader = csv.reader(f)
sorted_list = list(reader) # turn the reader iterator into a list
sorted_list.sort(key=lambda x: x[0]) # the first column as a sorting key, can be omitted
print("\n".join(str(row) for row in sorted_list)) # prettier print
或通過兩個鍵:
with open("studentinfo.txt", "r") as f:
reader = csv.reader(f)
sorted_list = list(reader) # turn the reader iterator into a list
sorted_list.sort(key=lambda x: (x[3], x[4])) # use fourth and fifth column
print("\n".join(str(row) for row in sorted_list)) # prettier print
您可以在list.sort()
調用中添加reverse=True
進行降序排序。
附件 -如果您確實不想使用lambda(為什么?),則可以定義一個項獲取函數(或僅使用為此目的而存在的operator.itemgetter
)並將其傳遞給list.sort()
調用,例如:
def get_third_column(x):
return x[2]
with open("studentinfo.txt", "r") as f:
reader = csv.reader(f)
sorted_list = list(reader) # turn the reader iterator into a list
sorted_list.sort(key=get_third_column) # use the third column as a sorting key
print("\n".join(str(row) for row in sorted_list)) # prettier print
一種緊湊,簡單的解決方案,可讀取->排序->寫入:
import csv
import operator
with open("input.csv") as fh:
reader = csv.reader(fh)
rows = sorted(reader, key=operator.itemgetter(0), reverse=True)
with open("output.csv", "w") as fh:
csv.writer(fh).writerows(rows)
要在控制台上打印而不是寫入文件,可以使用sys.stdout
作為文件句柄:
import sys
with sys.stdout as fh:
csv.writer(fh).writerows(rows)
operator.itemgetter(0)
確定要排序的字段。 第0個字段是ID。 要按姓氏排序,請使用operator.itemgetter(2)
,因為姓氏是第三列。
要按多個字段排序,您將需要使用lambda,例如按姓氏和名字排序:
rows = sorted(reader, key=lambda x: (x[2], x[1]), reverse=True)
您還可以改進排序之前要求用戶輸入ID的代碼:
id
隱藏了Python中的內置函數,因此不建議將其用作變量 您可以這樣寫:
with open("studentinfo.txt") as fh:
reader = csv.reader(fh)
student_id = input("Enter Id:")
for row in reader:
if row[0] == student_id:
print(row[1] + " " + row[2])
完成操作后,使用import運算符和一個可能的解決方案:注意-理想情況下,您需要一個標頭來區分要排序的內容(假設用戶想明確指定此內容)
import csv
import operator
ifile =open('myfile.csv', 'rb')
infile = csv.reader(ifile)
# Note that if you have a header, this is the header line
infields = infile.next()
startindex = infields.index('Desired Header')
# Here you are creating the sorted list
sortedlist = sorted(infile, key=operator.itemgetter(startindex), reverse=True)
ifile.close
# open the output file - it can be the same as the input file
ofile = open('myoutput.csv, 'wb')
outfile.writerow(infields)
for row in sortedlist:
outfile.writerow(row)
ofile.close()
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