How do I break numeric vector into variable length sections and combine in a matrix

Question

AndyT 2015-7-12

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https://ww2.mathworks.cn/matlabcentral/answers/229565-how-do-i-break-numeric-vector-into-variable-length-sections-and-combine-in-a-matrix

编辑： Azzi Abdelmalek 2015-7-12

采纳的回答： the cyclist

在 MATLAB Online 中打开

Hi , I am trying to prep some data and I need to manipulate a vector such as the example here , A

>> A=[1,4,15,56,58,59,68,79,3,45,12,34,62,90]

A = 1 4 15 56 58 59 68 79 3 45 12 34 62 90

I want to break the vector at every point that a value is less than its preceding value and create a matrix of the smaller sections so the example above would become

B=

1 4 15 56 58 59 68 79

3 45

12 34 62 90

The problem I am having is that the length of any ascending values section of the vector A is variable but typically cannot exceed 80 values. I can find the values in the vector to break at but don't know what kind of structure to use to collect the smaller sections in one object . Matlab needs a regular m x n matrix structure or throws errors about dimensions not being consistent .

Do I need to add zeros to the sections to make each one at least as long as the longest single run of values?

B would then look something like;

B =

   4    15    56    58    59    68    79
  45     0     0     0     0     0     0
  34    62    90     0     0     0     0

My coding skills fail me at this point so any help would be gratefully received. Thanks

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Answer 1

the cyclist 2015-7-12

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在 MATLAB Online 中打开

Here is a straightforward method to do this. I gave the variables explanatory names, to help guide you in what I am doing:

A = [1,4,15,56,58,59,68,79,3,45,12,34,62,90];
runStarts = [1 find(diff(A)<0)+1];
numberRuns = numel(runStarts);
runLengths = diff([runStarts numel(A)+1]);
B = zeros(numberRuns,max(runLengths));
for nr = 1:numberRuns
    B(nr,1:runLengths(nr)) = A(runStarts(nr):(runStarts(nr)+runLengths(nr)-1));
end

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AndyT 2015-7-12

Thanks so much Cyclist , I see how you have broken the problem into getting all the A sections identified first and then populating the B matrix on top of a zeros matrix. Super!

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Answer 2

Azzi Abdelmalek 2015-7-12

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/229565-how-do-i-break-numeric-vector-into-variable-length-sections-and-combine-in-a-matrix#answer_185826

编辑：Azzi Abdelmalek 2015-7-12

在 MATLAB Online 中打开

A=[1,4,15,56,58,59,68,79,3,45,12,34,62,90]
a= diff(A)<0;
idx1=[1 find(a)+1];
idx2=find([a 1]);
n=max(idx2-idx1)+1;
m=numel(idx1);
out=zeros(m,n);
for k=1:m
  ii=idx1(k):idx2(k);
  out(k,1:numel(ii))=A(ii);
end
out

Or

A=[1,4,15,56,58,59,68,79,3,45,12,34,62,90]
a= diff(A)<0;
idx1=[1 find(a)+1];
idx2=find([a 1]);
n=max(idx2-idx1)+1
out=cell2mat(arrayfun(@(x,y) [A(x:y) zeros(1,n-y+x-1)],idx1',idx2','un',0))