Python – Convert CSV to List of Lists - Finxter

To read a CSV to a nested list in pure Python, open the file using open('my_file.csv') , read all lines into a variable using f.readlines() . Skiptocontent Menu 4.7/5-(4votes) TableofContents ProblemFormulationMethod1:csv.reader()Method2:One-LinerMethod3:PandasMethod4:RawPythonNoDependencyMorePythonCSVConversionsPythonOne-LinersBook:MastertheSingleLineFirst! ProblemFormulation GivenaCSVfile(e.g.,storedinthefilewithname'my_file.csv'). INPUT:file'my_file.csv' 9,8,7 6,5,4 3,2,1 Challenge:Howtoconvertittoalistoflists(=nestedlist),i.e.,puttingtherowvaluesintotheinnerlists? OUTPUT:Pythonlistoflists [[9,8,7],[6,5,4],[3,2,1]] Method1:csv.reader() Method1:csv.reader() ToconvertaCSVfile'my_file.csv'intoalistoflistsinPython,usethecsv.reader(file_obj)methodtocreateaCSVfilereader.Thenconverttheresultingobjecttoalistusingthelist()constructor. Here’sasimpleexamplethatconvertsourCSVfiletoanestedlistusingthisapproach: importcsv csv_filename='my_file.csv' withopen(csv_filename)asf: reader=csv.reader(f) lst=list(reader) Output: print(lst) #[['9','8','7'],['6','5','4'],['3','2','1']] Method2:One-Liner Method2:One-Liner YoucanalsoconvertaCSVtoalistoflistsusingthefollowingPythonone-linerthatopensthefileusingopen(),passesthefileobjectintothecsv.reader()function,andconverttheCSVreaderobjecttoalistusingthelist()built-infunctioninPython. Here’showthatlooks: importcsv;lst=list(csv.reader(open('my_file.csv')));print(lst) Concise,isn’tit?🙂 Theoutputisthesame: [['9','8','7'],['6','5','4'],['3','2','1']] Bytheway:Doyouneedallinnerelementsconvertedtoacertaindatatypesuchasinteger? Ifso,usethefollowingapproachontopofthenestedlistofstrings,lst,obtainedfromthepreviousmethods: new_lst=[[int(x)forxininner]forinnerinlst] Theconvertednew_lstnowcontainsanestedlistofints: print(new_lst) #[[9,8,7],[6,5,4],[3,2,1]] Method3:Pandas Method3:Pandas YoucanconvertaCSVtoalistoflistswithPandasbyfirstreadingtheCSVwithoutheaderlineusingpd.read_csv('my_file.csv',header=None)functionandsecondconvertingtheresultingDataFrametoanestedlistusingdf.values.tolist(). Here’sanexamplethatconvertstheCSVtoaPandasDataFrameandthentoanestedrawPythonlist: importpandasaspd df=pd.read_csv('my_file.csv',header=None) lst=df.values.tolist() print(lst) #[[9,8,7],[6,5,4],[3,2,1]] Thiswaseasy,wasn’tit?🙂 Ofcourse,youcanalsoone-linerizeitbychainingcommandslikeso: lst=pd.read_csv('my_file.csv',header=None).values.tolist() Method4:RawPythonNoDependency Method4:RawPythonNoDependency Ifyou’relikeme,youtrytoavoidusingdependenciesiftheyarenotneeded.RawPythonisoftenmoreefficientandsimpleenoughanyways.Also,youdon’topenyourselfupagainstunnecessaryrisksandcomplexities. Question:So,isthereasimplewaytoreadaCSVtoalistoflistsinrawPythonwithoutexternaldependencies? Sure! ToreadaCSVtoanestedlistinpurePython,openthefileusingopen('my_file.csv'),readalllinesintoavariableusingf.readlines().Now,iterateoveralllines,stripthemfromwhitespaceusingstrip(),andsplitthemonthedelimiter','usingsplit(','). Youcanaccomplishthisinasimplelistcomprehensionstatementlikeso: csv_filename='my_file.csv' withopen(csv_filename)asf: lines=f.readlines() lst=[line.strip().split(',')forlineinlines] print(lst) FeelfreetocheckoutmydetailedvideoincaseyouneedarefresheronthepowerfulPythonconceptlistcomprehension: ASimpleIntroductiontoListComprehensioninPython 🌍RelatedTutorial:UnderstandingListComprehensioninPython. MorePythonCSVConversions 🐍LearnMore:Ihavecompiledan“ultimateguide”ontheFinxterblogthatshowsyouthebestmethod,respectively,toconvertaCSVfiletoJSON,Excel,dictionary,Parquet,list,listoflists,listoftuples,textfile,DataFrame,XML,NumPyarray,andlistofdictionaries. BecomeaOne-LinerWizard! Incaseyouenjoyedtheone-linerspresentedhereandyouwanttoimproveyourPythonskills,feelfreetogetyourselfacopyofmybest-sellingPythonbook: PythonOne-LinersBook:MastertheSingleLineFirst! Pythonprogrammerswillimprovetheircomputerscienceskillswiththeseusefulone-liners. PythonOne-Linerswillteachyouhowtoreadandwrite“one-liners”:concisestatementsofusefulfunctionalitypackedintoasinglelineofcode.You’lllearnhowtosystematicallyunpackandunderstandanylineofPythoncode,andwriteeloquent,powerfullycompressedPythonlikeanexpert. Thebook’sfivechapterscover(1)tipsandtricks,(2)regularexpressions,(3)machinelearning,(4)coredatasciencetopics,and(5)usefulalgorithms. Detailedexplanationsofone-linersintroducekeycomputerscienceconceptsandboostyourcodingandanalyticalskills.You’lllearnaboutadvancedPythonfeaturessuchaslistcomprehension,slicing,lambdafunctions,regularexpressions,mapandreducefunctions,andsliceassignments. You’llalsolearnhowto: Leveragedatastructurestosolvereal-worldproblems,likeusingBooleanindexingtofindcitieswithabove-averagepollutionUseNumPybasicssuchasarray,shape,axis,type,broadcasting,advancedindexing,slicing,sorting,searching,aggregating,andstatisticsCalculatebasicstatisticsofmultidimensionaldataarraysandtheK-MeansalgorithmsforunsupervisedlearningCreatemoreadvancedregularexpressionsusinggroupingandnamedgroups,negativelookaheads,escapedcharacters,whitespaces,charactersets(andnegativecharacterssets),andgreedy/nongreedyoperatorsUnderstandawiderangeofcomputersciencetopics,includinganagrams,palindromes,supersets,permutations,factorials,primenumbers,Fibonaccinumbers,obfuscation,searching,andalgorithmicsorting Bytheendofthebook,you’llknowhowtowritePythonatitsmostrefined,andcreateconcise,beautifulpiecesof“Pythonart”inmerelyasingleline. GetyourPythonOne-LinersonAmazon!! ChrisWhileworkingasaresearcherindistributedsystems,Dr.ChristianMayerfoundhisloveforteachingcomputersciencestudents. TohelpstudentsreachhigherlevelsofPythonsuccess,hefoundedtheprogrammingeducationwebsiteFinxter.com.He’sauthorofthepopularprogrammingbookPythonOne-Liners(NoStarch2020),coauthoroftheCoffeeBreakPythonseriesofself-publishedbooks,computerscienceenthusiast,freelancer,andownerofoneofthetop10largestPythonblogsworldwide. Hispassionsarewriting,reading,andcoding.ButhisgreatestpassionistoserveaspiringcodersthroughFinxterandhelpthemtoboosttheirskills.Youcanjoinhisfreeemailacademyhere. RelatedTutorialsTheUltimateGuidetoPythonListsPythonListofLists-AHelpfulIllustratedGuidetoNested…56PythonOne-LinerstoImpressYourFriendsPythonOneLineXPythonJoinList[UltimateGuide]TheUltimateGuideonConvertingaCSVinPython WhyFinxter? 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