Splitting array based on a single column's condition

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yz
yz 2017-12-19
评论： Star Strider 2018-1-3
Hello, I am trying to separate my large array of [n rows, 5 columns] into individual arrays of [k rows, 5 columns] (where k < n). I want to split my array based on numbers on my fourth column. The fourth column has numbers that increase and decrease in a loop to create some peaks (example: goes from 0 to 35, then from 35 goes to 0, then from 0 to -35, etc.).
I've attached a sample code to help better explain what I mean.
Is there an efficient way to split these data? (So far I've been going into the data selecting where I want to split them up, and doing it manually.)
Thank you in advance.

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Ramnarayan Krishnamurthy
编辑：Ramnarayan Krishnamurthy 2017-12-28
If the transition point in the fourth column is known to be 0, then you can consider splitting the data by the location of these 0's.
% Locate the zeros in the 4th column
index_0 = find(s_P1_5(:,4)==0);
% Include the start and end indices
idx = [0 index_0' size(s_P1_5,1)];
% Create individual cells containing the sub matrices
out = mat2cell(s_P1_5, diff(idx))
The split arrays will now be stored in out{1}, out{2} and so on.
  1 个评论
yz
yz 2018-1-3
This is awesome, thank you! Though, I'm trying to modify your code such that the division happens at the peaks, zeroes, and valleys of column 4. Is there a way to make that new cell output be?:
  • cell1: peak to zero
  • cell2: zero to valley
  • cell3: valley to zero
  • cell4: zero to peak
  • cell5: peak to zero, etc.
This is what I've done:
% Locate the zeros in the 4th column
index_0 = find(s_P1_30(:,4)==0);
% Find peaks
index_1 = find(s_P1_30(:,4)==max(s_P1_5(:,4)));
% Find valleys
index_2 = find(s_P1_30(:,4)==min(s_P1_5(:,4)));
% Include the start and end indices
idx = [0 index_0' index_1' index_2' size(s_P1_5,1)];
% Create individual cells containing the sub matrices
out = mat2cell(s_P1_5, diff(idx))
But I'm getting the wrong output. Instead of making the correct cells, I'm taking one huge cells at the end. Is there a way to fix this?
Thank you again!

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