How to read values for the range between each maximum and each minimum from a large uneven data file?

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Madan Kumar 2020-7-27

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编辑： per isakson 2020-7-28

采纳的回答： per isakson

axn.txt

在 MATLAB Online 中打开

Hi,

I have a data file with 11000 rows and 4 columns. I need to read all values (in all columns) for data between each maximum and each minimum of column 3. Integrate column 3 and column 4, and calculate the mean of column 2, for each range between the maximum and minimum of column 3. Do I make sense?? I am really unsure about how to start. I am using Matlab2015a. I have attached what I want to do as image. For rudimentary case I can do like shown on the right in figure. But it would take a decade to solve. Need help.

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KSSV 2020-7-27

You want to do this by splitting at every sixth row?

Madan Kumar 2020-7-27

No, the data is uneven. some times it's 5 rows, sometimes 6 rows and so on..

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Answer 1

per isakson 2020-7-27

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https://ww2.mathworks.cn/matlabcentral/answers/571027-how-to-read-values-for-the-range-between-each-maximum-and-each-minimum-from-a-large-uneven-data-file#answer_471289

编辑：per isakson 2020-7-27

在 MATLAB Online 中打开

"range between the maximum and minimum of column 3" with a bit of guessing my interpretation is implemented in ixb and ixe

%%
fid = fopen('axn.txt','r');
cac = textscan( fid, '%f%f%f%f', 'CollectOutput',true );
num = cac{1};
[~] = fclose( fid );
%%
ixb = [ 1; find(diff(num(:,3))>0)+1 ];  % beginning of section
ixe = [ ixb(2:end)+1; size(num,1) ];    % end of section
%%
len = length( ixb );
result = nan( len, 2 ); 
for jj = 1 : len
    result(jj,1) = mean(num(ixb(jj):ixe(jj),2));
    result(jj,2) = trapz(num(ixb(jj):ixe(jj),3),num(ixb(jj):ixe(jj),4));
end

outputs

>> result
result =
       51.494      -10.433
       51.472      -23.332
       51.479     -0.95127
       51.463      -29.865
>> 

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per isakson 2020-7-27

编辑：per isakson 2020-7-28

在 MATLAB Online 中打开

Is this better?

>> result
result =
       51.492      -24.937
       51.463      -29.865
       51.472      -24.485
       51.463      -29.865
>> 

My mistake. Replace

ixe = [ ixb(2:end)+1; size(num,1) ];

by

ixe = [ ixb(2:end)-1; size(num,1) ];

with a minus one, not plus.

Now the beginings and ends of the "sections" agree with my intention

>> ixb', ixe'
ans =
     1     6    12    18
ans =
     5    11    17    23
>> 

Madan Kumar 2020-7-27

Thank you so much. It works.

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How to read values for the range between each maximum and each minimum from a large uneven data file?

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