how to read selected data from text file matlab ?

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pruth 2018-8-16

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编辑： pruth 2018-8-17

采纳的回答： jonas

2jan.txt

hi, I have this text file. (attached).

from this text file I only want read only second column(date), third column(time) and the last column. first 11 rows can be deleted. since time and date are two different column I am not able to combine them and make single vector. I just want do hourly average which I can do for sure. but I can not read and collect the data from this file in the first place. I Hope you understand my question. thanks

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jonas 2018-8-16

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编辑：jonas 2018-8-16

在 MATLAB Online 中打开

readtable can do this for you easily.

%%Read the relevant columns, exclude 10 rows
opts=detectImportOptions('str.txt','NumHeaderLines',10);
opts.SelectedVariableNames = {'timestamp','RPM','absE_f'};
opts = setvartype(opts,{'timestamp','RPM'},{'datetime','duration'})
T=readtable('str.txt',opts)
t=T.timestamp+T.RPM;

readtable automatically detects the datetime and duration format of columns 2 and 3. If it fails, you can specify the format in detectImportOptions. Now, just build a timetable:

TT=timetable(t,T.absE_f)

ans =

10×1 timetable
             t                Var1  
    ____________________    ________
    02-Jan-2006 00:00:00      131.96
    02-Jan-2006 00:00:10    -0.26753
    02-Jan-2006 00:00:20    -0.29573
    02-Jan-2006 00:00:30      127.73

Finally,

TT2 = retime(TT,'hourly','mean')

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pruth 2018-8-17

在 MATLAB Online 中打开

out put

>> opts=detectImportOptions('2jan.txt','NumHeaderLines',10)

opts =

DelimitedTextImportOptions with properties:
   Format Properties:
                    Delimiter: {'\t'}
                   Whitespace: '\b '
                   LineEnding: {'\n'  '\r'  '\r\n'}
                 CommentStyle: {}
    ConsecutiveDelimitersRule: 'split'
        LeadingDelimitersRule: 'keep'
                EmptyLineRule: 'skip'
                     Encoding: 'windows-1252'
   Replacement Properties:
                  MissingRule: 'fill'
              ImportErrorRule: 'fill'
             ExtraColumnsRule: 'addvars'
   Variable Import Properties:   Set types by name using setvartype
                VariableNames: {'DOY', 'timestamp', 'RPM' ... and 5 more}
                VariableTypes: {'double', 'datetime', 'char' ... and 5 more}
        SelectedVariableNames: {'DOY', 'timestamp', 'RPM' ... and 5 more}
              VariableOptions: Show all 8 VariableOptions 
  Access VariableOptions sub-properties using setvaropts/getvaropts
   Location Properties:
                     DataLine: 12
            VariableNamesLine: 11
               RowNamesColumn: 0
            VariableUnitsLine: 0
     VariableDescriptionsLine: 0

pruth 2018-8-17

thank you so much , Jonas, for your time and patience !!

jonas 2018-8-17

在 MATLAB Online 中打开

Yes sorry, my bad. Grab the time by

datenum(TT.t)

No problem! Happy to help.

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pruth 2018-8-17

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编辑：pruth 2018-8-17

在 MATLAB Online 中打开

final code. !!

clear all
close all 
clc
opts=detectImportOptions('2jan.txt','NumHeaderLines',10); %%%Read the relevant columns, exclude 10 rows
opts.SelectedVariableNames = {'timestamp','RPM','absE_f'};
opts = setvartype(opts,'timestamp','datetime');
opts = setvartype(opts,'RPM','datetime');
opts = setvaropts(opts,'timestamp','InputFormat','MM/dd/yyyy');
opts = setvaropts(opts,'RPM','InputFormat','HH:mm:SS');
T=readtable('2jan.txt',opts);
Date=datetime(T.timestamp,'format','yyyy-MM-dd hh:mm:SS');
TimeOfDay=hours(hour(T.RPM))+minutes(minute(T.RPM))+seconds(second(T.RPM));
t=Date+TimeOfDay;
TT=timetable(t,T.absE_f);
TT2 = retime(TT,'hourly','mean');
final(:,1)=datenum(TT2.t(:,1));
final(:,2)= TT2.Var1(:,1);