How to split data matrix conditionally?

Question

Andi 2022-4-14

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https://ww2.mathworks.cn/matlabcentral/answers/1696115-how-to-split-data-matrix-conditionally

评论： Andi 2022-4-14

I have a data matrix of 59 columns and variabale number of rows, Required to extract a new matrix such that it include only those values that are in a specific bound.

As a result, we left with variable number of observations in each coloumn. How can i get new matrix, in such a condition:

An examplry random data set with my approach as below, but did not get required results.

p = rand(10, 10)
for i=1:10
    q = p((p(:,ii) > .2) & (p(:,ii) < .4) , :)
end 

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Answer 1

Chunru 2022-4-14

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https://ww2.mathworks.cn/matlabcentral/answers/1696115-how-to-split-data-matrix-conditionally#answer_942405

编辑：Chunru 2022-4-14

在 MATLAB Online 中打开

You will not get an matrix for the output since the number of entries satisfying the condition for each column will be different.

Your output can be combined as a cell array instead.

n = 50;
p = rand(n, n);
for i=1:n
    pi = p(:, i);
    q{i} = pi(pi > .2 & pi < .4);
end 
q
q = 1×50 cell array
    {13×1 double}    {13×1 double}    {9×1 double}    {12×1 double}    {11×1 double}    {6×1 double}    {9×1 double}    {14×1 double}    {8×1 double}    {13×1 double}    {10×1 double}    {9×1 double}    {9×1 double}    {10×1 double}    {8×1 double}    {10×1 double}    {17×1 double}    {10×1 double}    {14×1 double}    {11×1 double}    {9×1 double}    {7×1 double}    {5×1 double}    {9×1 double}    {8×1 double}    {12×1 double}    {12×1 double}    {14×1 double}    {9×1 double}    {7×1 double}    {5×1 double}    {13×1 double}    {9×1 double}    {10×1 double}    {10×1 double}    {15×1 double}    {9×1 double}    {13×1 double}    {12×1 double}    {9×1 double}    {11×1 double}    {13×1 double}    {10×1 double}    {6×1 double}    {12×1 double}    {11×1 double}    {12×1 double}    {10×1 double}    {11×1 double}    {10×1 double}
%% counting base on q (actually you can do that on p instead)
count = cellfun(@numel, q)
count = 1×50
    13    13     9    12    11     6     9    14     8    13    10     9     9    10     8    10    17    10    14    11     9     7     5     9     8    12    12    14     9     7
% number of cells with >=10 elements
nc = sum(count>=10)
nc = 31

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Chunru 2022-4-14

编辑：Chunru 2022-4-14

在 MATLAB Online 中打开

It seems that you need to change your U and L so some data are selected.

data1=readmatrix('https://www.mathworks.com/matlabcentral/answers/uploaded_files/963815/data1.csv'); % selected candidate earthquake
ev_time=datenum(data1(:,1),data1(:,2),data1(:,3),data1(:,4),data1(:,5),data1(:,6));
cand_ev=ev_time';
for jj=1:194
     b=cand_ev(:,jj);
     aa(jj)= addtodate(b, 30, 'day');
     bb(jj)= addtodate(b, -30, 'day');
end 
U_lim=aa
U_lim = 1×194
1.0e+05 *

    7.3604    7.3604    7.3608    7.3611    7.3611    7.3611    7.3611    7.3612    7.3612    7.3612    7.3613    7.3613    7.3613    7.3613    7.3614    7.3614    7.3614    7.3615    7.3615    7.3616    7.3619    7.3619    7.3620    7.3620    7.3625    7.3625    7.3625    7.3625    7.3631    7.3631
L_lim=bb
L_lim = 1×194
1.0e+05 *

    7.3598    7.3598    7.3602    7.3605    7.3605    7.3605    7.3605    7.3606    7.3606    7.3606    7.3607    7.3607    7.3607    7.3607    7.3608    7.3608    7.3608    7.3609    7.3609    7.3610    7.3613    7.3613    7.3614    7.3614    7.3619    7.3619    7.3619    7.3619    7.3625    7.3625
b=readmatrix('https://www.mathworks.com/matlabcentral/answers/uploaded_files/963820/selected_0.01.csv');
%a = b(~isnan(b));
keep = sum(~isnan(b), 1) >= 100
keep = 1×10 logical array
   1   1   1   1   1   1   1   1   1   1
a = b(:, keep);
any(isnan(a))
ans = 1×10 logical array
   1   1   1   1   1   1   1   1   1   1
U=U_lim(:,8)
U = 7.3612e+05
L=L_lim(:,1)
L = 7.3598e+05
whos
  Name             Size               Bytes  Class      Attributes

  L                1x1                    8  double               
  L_lim            1x194               1552  double               
  U                1x1                    8  double               
  U_lim            1x194               1552  double               
  a            45000x10             3600000  double               
  aa               1x194               1552  double               
  ans              1x10                  10  logical              
  b            45000x10             3600000  double               
  bb               1x194               1552  double               
  cand_ev          1x194               1552  double               
  data1          194x6                 9312  double               
  ev_time        194x1                 1552  double               
  jj               1x1                    8  double               
  keep             1x10                  10  logical              
for kk=1:size(a,2)     % 59 is too big for your data
    ai = a(:, kk);   % get the column
    ai(isnan(ai)) = [];     % remove nan
    e{kk}=a(ai>L & ai<U);
    %q = a((a(:,kk) > L) & (a(:,kk) < U) , :   );
end
count = cellfun(@numel, e)
count = 1×10
          91         129         175         110         276         775         660        1218        2144         424

Andi 2022-4-14

For each point in data set, I have an upper and lower limit, then by using that upper and lower limits i need to search for observations in ecah coloumn of dataset 2. So technically each column should have some value or just no value. There is no other choice to give answer like NaN or etc.

Andi 2022-4-14