Reading a massive file but skipping several lines / rows at a fixed interval

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L'O.G. 2022-3-29

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评论： KSSV 2022-3-29

What is the most efficient way to read / analyze rows 1-1990 of an array, then skip 9 lines, then read rows 2000-3990, skip 9 rows, read rows 4000-5990, and so on to the end of the array? Is there a way to vectorize that?

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L'O.G. 2022-3-29

Yes, but how? I know how to delete every 4th row, for example, would be A(4:4:end,:) = [] but I don't know how to apply that for my case where I need to skip / delete multiply lines.

Stephen23 2022-3-29

编辑：Stephen23 2022-3-29

Use a loop. Inside the loop you can easily tell MATLAB which part of the file to read, e.g.:

TEXTSCAN lets you specify how many times the format is applied and how many header lines.
READTABLE et al let you specify the data location, header location, etc.

What is so special about the rows you wan to ignore: are they intermediate headers or just data you don't want? The answer to that question will change how you can approach this task.

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Answer 1

KSSV 2022-3-29

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编辑：KSSV 2022-3-29

在 MATLAB Online 中打开

id = 1:9 ;  % line numbers 
V = 1990:2000:9990 ;  % give the end wisely 
idx = id'+V ;  % make indices 
idx = idx(:) ;  % make indices a column 
% Let A be your array 
A(idx) = [] ;    % remove the lines using the indices 

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L'O.G. 2022-3-29

Thanks. Very nice. One small typo: the last line should be: A(idx,:) = [];

KSSV 2022-3-29

Yes, if it is an array use A(idx), if it is a matrix, A(idx,:). I have considered it as an array. :)

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Answer 2

Arif Hoq 2022-3-29

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在 MATLAB Online 中打开

try this loop:

A=(1:9990)';　% making an array
idx=2000;   % taken value from 2000
count=(size(A,1)+10)/idx;
first_index=A(1:1990);  % first index value to make the loop simple
C=cell(count,1);
for i=2:count
    C{i}=A(idx*(i-1):(idx*i)-10);    
end
mat=[C{:}]