using function with loop

Question

sermet OGUTCU 2021-4-26

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/813895-using-function-with-loop

评论： sermet OGUTCU 2021-4-27

function [b, n, index] = RunLength(x)
d = [true; diff(x(:)) ~= 0];  % TRUE if values change
b = x(d);                     % Elements without repetitions
k = find([d.', true]);        % Indices of changes
n = diff(k);                  % Number of repetitions
index = k(1:numel(k) - 1);
if iscolumn(x)
    n     = n.';
    index = index.';
end
end
data = [1.2;1.0;0.05;0.4;0.3;0.2;0.1;0.05;0.04;0.03;0.03;0.02;0.01;0.001;0.01;0.01;0.001 ] ;
[b, n, index] = RunLength(data < 0.1);
match = find(b & n >= 10, 1);
result = index(match)
% This function find the number of row which 10 consecutive rows from the
% this computed row are smaller than 0.10. The result equals 8th row.

I need to use this function with loop such as;

data= 605x1 array includes numeric data

I need to compute the "result" with every 121 rows within 605 rows. So I need to run RunLength function five times (to produce five different result ) using the every 121 rows of the "data". I tried the below codes but it doesn't work;

i=1:121:605
for j=5
[b(:,j), n(:,j), index(:,j)] = RunLength(abs(data(i(j))) < 0.1);
match(j) = find(b(:,j) & n(:,j) >= 10, 1);
result(j) = index(match)
end

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Answer 1

Jan 2021-4-26

1
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/813895-using-function-with-loop#answer_685365

编辑：Jan 2021-4-26

在 MATLAB Online 中打开

Result = zeros(1, 5);
iResult = 0;
for k = 1:121:605
  datak = data(k:k+120);
  [b, n, index] = RunLength(datak < 0.1);
  match = find(b & n >= 10, 1);
  
  iResult         = iResult + 1;
  Result(iResult) = index(match);
end

Maybe you have to catch the case, that match is empty.

Alternatively:

Result  = zeros(1, 5);
iResult = 0;
for k = 1:5
  index = (k - 1)*121 + 1;
  datak = data(k:k+120);
  [b, n, index] = RunLength(datak < 0.1);
  match = find(b & n >= 10, 1);
  Result(k) = index(match);
end

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sermet OGUTCU 2021-4-27

在 MATLAB Online 中打开

data.txt

Dear @Jan

The attached file is the original data file (53361 x 1). When using the second part of your codes as;

size_data=numel(data);
repitition=size_data/121; 
Result = zeros(1, repitition);
iResult = 0;
for k = 1:121:size_data
  index = (k - 1)*121 + 1;
  datak = abs(data(k:k+120));
  [b, n, index] = RunLength(datak < 0.1);
  match = find(b & n >= 10, 1);
  Result(k) = index(match);
end

It produces "Improper assignment with rectangular empty matrix." this error.

When the first part of your codes worked, two problem arises. One is the 53361/121=441 Results need to be created, whereas 377 Results are created, the other remaning Results are equal 0. The second one is, third Results are computed as NaN, whereas it should be 7 in according with the real data. I applied the first part of your code as follows;

size_data=numel(data);
repitition=size_data/121;
Result = zeros(1, repitition);
iResult = 0;
for k = 1:121:size_data
  datak = abs(data(k:k+120));
  [b, n, index] = RunLength(datak < 0.1);
  match = find(b & n >= 20, 1);
if isempty(match)
   Result(iResult) = NaN;
else
   iResult         = iResult + 1; 
   Result(iResult) = index(match); 
end
end

Jan 2021-4-27

编辑：Jan 2021-4-27

在 MATLAB Online 中打开

"Improper assignment with rectangular empty matrix." - this is the already mentioned problem, when match is empty. In the 2nd code you'd need to insert the isempty(match) check also.

You need to advance iResult even if match is empty:

size_data=numel(data);
repitition=size_data/121;
Result = zeros(1, repitition);
iResult = 0;
for k = 1:121:size_data
  datak = abs(data(k:k+120));
  [b, n, index] = RunLength(datak < 0.1);
  match = find(b & n >= 20, 1);
  iResult = iResult + 1;   % Before the IF ISEMPTY(match) check
  if isempty(match)
    Result(iResult) = NaN;
  else
    Result(iResult) = index(match); 
  end
end

Or slightly simplified:

size_data=numel(data);
repitition=size_data/121;
Result = NaN(1, repitition);   % NaN as default
iResult = 0;
for k = 1:121:size_data
  datak = abs(data(k:k+120));
  [b, n, index] = RunLength(datak < 0.1);
  match = find(b & n >= 20, 1);
  iResult = iResult + 1;
  if ~isempty(match)
     Result(iResult) = index(match); 
  end
end