selection of data from matrix

I have a dataset lets say a matrix of 100 rows and 5 columns, each row represents a dataset.Now I want to select 5 any rows(datasets) initially, then further I want to select 4 rows(dataset) except initially 5 rows should not be repeated, then next I want to select 10 rows except for initially selected rows (those 9 rows should not be repeated here) in before and so on..... one thing to remember that one rows should be selected once here.

Answer 1

[Andrei Bobrov]

data = randi([-41 78],100,5);

ii = randperm(size(data,1));
k = [5 4 10];
out = mat2cell(data(ii(1:sum(k)),:),k,size(data,2));

[MUKESH KUMAR]

short and sweet answer, thanks

Answer 2

[KL]

One easy alternative is to shuffle the row of your matrix first and then extract them from top to bottom,

 data = [(1:100).' rand(100,5)]; %dummy data
 indx = randperm(size(data,1));
 data = data(indx,:);
 numberofRowsWanted = 4;
 data_ext = data(1:numberofRowsWanted,:);

Another alternative is to split and put them all in a cell array.

data = [(1:100).' rand(100,5)]; %dummy data
indx = randperm(size(data,1)); %generate random indices without repeating
splits = [4,5,10]; %how many rows you want to extraxt each time, extend it as you wish
%now, use arrayfun to extract those rows and store them in a cell array.
data_ext = arrayfun(@(x,y) data(indx(x:y),:),[1 splits+1],[splits(1) splits(1:end-1)+splits(2:end)],'uni',0);

Answer 3

[KSSV]

Check the below example code:

K = 1:100 ;
pick = [5 4 9 10] ;
for i = 1:length(pick)
    take = randsample(K,pick(i)) 
    % remove the selected numbers 
    K = setdiff(K,take) ;
end

[MUKESH KUMAR]

if the size of K matrix like 100*5 then this code doesn't work.any further solution for it , Thanks

[KL]

It indeed works, in fact all of the solutions here do what you want, they are just examples. Instead of just copy-pasting, try and understand how it works.

Answer 4

[Guillaume]

There are many ways you could do this. You could keep track of the row you've selected and exclude them from the set of rows to select from, but probably the simplest way would be to remove the rows you've selected from your dataset.

dataset = rand(100, 5);  %demo dataset
while ~isempty(dataset)
   %select 5 rows at random:
   numrowstoselect = 5;  %adjust as required
   selectedrows = randperm(size(dataset, 1), min(numrowstoselect, size(dataset, 1));
   selecteddataset = dataset(selectedrows, :);
   %remove selected rows from dataset so they can't be selected again
   dataset(selectedrows, :) = []; 
end