How to extract specific rows & columns from a text file

Question

Farhan K 2020-3-25

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编辑： per isakson 2020-3-27

I need to extract all the net names and toggle rates from a text file. total 179456 nets. Below screenshot is the few row and columns shown as example

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Farhan K 2020-3-26

I provided a screenshot as example

Farhan K 2020-3-26

Example.txt

Here is an example

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Answer 1

per isakson 2020-3-26

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/512983-how-to-extract-specific-rows-columns-from-a-text-file#answer_421968

编辑：per isakson 2020-3-26

See Read formatted data from text file or string and try

fileID = fopen(filename);
net_names = textscan( fileID, '%s%*f%*f%f%*f', 'Headerlines',3 );
fclose(fileID);

Added later. The script

%%
filename = 'd:\m\cssm\Example.txt';
fileID = fopen(filename);
net_names = textscan( fileID, '%s%*f%*f%f%*f', 'Headerlines',4 );
fclose(fileID);
%%
net_names{1}(1:3,1)
net_names{2}(1:3,1)

outputs

ans =
  3×1 cell array
    {'AES/r8/t0/t3/s4/n885'}
    {'AES/r3/p21[25]'      }
    {'AES/r7/z0[6]'        }
ans =
       0.0001
       0.0001
       0.0001

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per isakson 2020-3-26

编辑：per isakson 2020-3-27

"All table variables must have the same number of rows." tells me that textscan() fails to read your large file to its end. The reason is most likely that there is a line in your data file that doesn't match the format string. (I think readtable() will encounter the same problem. Might differ between releases. I run R2018b)

I reproduced your error by modifying line 44 of Example.txt to

AES/s3[124] 16.927 0.496 whats wrong

Next step is to add 'ReturnOnError' to the call of textscan()

net_names = textscan( fileID, '%s%*f%*f%f%*f'   ...
                    , 'Headerlines',4           ...
                    , 'ReturnOnError', false    ...    
                );

Now I get the error message

Error using textscan
Mismatch between file and format character vector.
Trouble reading 'Numeric' field from file (row number 40, field number 4) ==> whats       wrong\n
Error in cssm (line 4)
net_names = textscan( fileID, '%s%*f%*f%f%*f'   ...

which tells me that the two words, 'whats' and 'wrong', cause the error.

The cure to this error is to add 'TreatAsEmpty' to the call of textscan()

net_names = textscan( fileID, '%s%*f%*f%f%*f'               ...
                    , 'Headerlines',    4                   ...
                    , 'ReturnOnError',  false               ...
                    , 'TreatAsEmpty',   {'whats','wrong'}   ...
                );            

Problem solved. textscan reads the modified Example.txt without problems. The words, 'whats' and 'wrong', are converted to nan.

.

So far I've missed your attachment.

When browsing switching_prob_report.txt in the free editor notepad++ , I quickly spotted problematic lines at the end of the file. (There might be more.)

...
Trigger/n7                 2.780    0.000    0.49e-7  9.772e-08  
AES/*Logic0*             288.088    0.000    0.0000      0.0000  d
AES/*Logic1*              71.396    1.000    0.0000      0.0000  d
Tj_Trig                    7.086    0.000    0.0000      0.0000  
...
Trojan/lfsr/n25            2.489    0.000    0.0000      0.0000  
--------------------------------------------------------------------------------
Total (179456 nets)                                         24.1493 uW
1

We can solve the problem with the extra column containing the letter 'd' by modifying the format string to skip to the end of line after the 'Togglerates' column.

%%
filename = 'd:\m\cssm\switching_prob_report.txt';
fileID = fopen(filename);
net_names = textscan( fileID, '%s%*f%*f%f%*[^\n]'   ...
                    , 'Headerlines',    612         ...
                    , 'ReturnOnError',  true        ...
                );
fclose(fileID);

reads all data lines and fails (as expected) on the three last lines.

>> net_names{1}(end-4:end)
ans =
  5×1 cell array
    {'Trojan/lfsr/n21'                                                                 }
    {'Trojan/lfsr/n24'                                                                 }
    {'Trojan/lfsr/n25'                                                                 }
    {'--------------------------------------------------------------------------------'}
    {'Total'                                                                           }
>> net_names{2}(end-4:end)
ans =
     0
     0
     0
     0
   NaN
>>

The first column has one element more than the second. Without exactly understanding this result, I delete the elements, which originate in the footer.

%%
net_names{1}(end-1:end)= [];
net_names{2}(end) = [];

Farhan K 2020-3-27

wow! This is why I preferred to use MATLAB rather than using Python. Excellent help

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Answer 2

Akira Agata 2020-3-26

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https://ww2.mathworks.cn/matlabcentral/answers/512983-how-to-extract-specific-rows-columns-from-a-text-file#answer_421974

编辑：Akira Agata 2020-3-26

Thank you for uploading an example. How about the following?

% Read from text data
T = readtable('Example.txt','HeaderLines',4,'Format','%s%f%f%f%f');
T.Properties.VariableNames = {'Net','NetLoad','StaticProb','ToggleRate','SwPower'};
% Extract NetLoad and ToggleRate
T = T(:,{'Net','ToggleRate'});

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Farhan K 2020-3-26

In this file, if you go down, then you can find the Net and Toggle rate section with total 179456 nets

Akira Agata 2020-3-26

编辑：Akira Agata 2020-3-26

Thank you for attaching the data.

OK. Looking at your data, I found some irregular lines and needs to some pre-processing.

How about the following?

% Read from text data
C = readcell('switching_prob_report.txt','Delimiter','\r\n','NumHeaderLines',612);
% Delete the last 3 lines (because they don't contain data)
C(end-2:end) = [];
% Detect irregular lines (which does not end with number)
idx = ~endsWith(C,compose('%d',0:9));
% Delete characters at the end of the detected lines
C(idx) = regexprep(C(idx),'\s*[^\d]$','');
% Split the line
D = split(C);
% Extract 1st and 4th column
Net = D(:,1);
ToggleRate = str2double(D(:,4));