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matlabresampling
John legend2
John legend2

Reputation: 920

resample data based on a particular variable

I have a large dataset as below. From the data, I want to randomly sample based on 'id'. Since the data has 5 ids, I would like to sample 5 ids with replacement and produce a new dataset with observations of sampled ids. 

 id value   var1    var2    …
  1 1           
  1 2           
  1 3           
  1 4           
  2 5           
  2 6           
  2 7           
  3 8           
  3 9           
  3 10          
  4 11          
  4 12          
  4 13          
  5 14          
  5 15          
  5 16

Let's suppose, I randomly draw 5 values from 1 to 5 (because there are 5 unique ids) and the result is (2 4 3 2 1). Then, I would like to have this data

  id    value   var1    var2    …
  2 5           
  2 6           
  2 7           
  4 11          
  4 12          
  4 13          
  3 8           
  3 9           
  3 10          
  2 5           
  2 6           
  2 7           
  1 1           
  1 2           
  1 3           
  1 4

Upvotes: 0

Views: 68

Answers (1)

Nakini
Nakini

Reputation: 772

Here is a sample code for ids varying from 1 through 5.

% data = [1 1; 1 2; 1   3; 1 4; 2 5; 2 6; 2 7; 3 8; 3 9; 3 10; 4 11; 4 12; 4 13;...
%     5 14; 5   15; 5 16];
data = rand(10000000,10);
data(:,1) = randi([1,5], length(data),1);

% Get all the indices from the 1st column;
indxCell = cell(5,1);
for i=1:5
    tmpIndx = find(data(:,1) == i);
    indxCell{i} = tmpIndx;
end

% Rearrange the indices
randIndx = randperm(5);
randIndxCell = indxCell(randIndx, 1);

% Generate a vector of indices by rearranging the 1st column of data matrix. 
numDataPts = length(data);
newIndices = zeros(numDataPts,1);
endIndx = 1;
for i=1:5
    startIndx = endIndx;
    endIndx = startIndx + length(randIndxCell{i});
    newIndices(startIndx:endIndx-1, 1) = randIndxCell{i};
end

newData = data(newIndices,:);

For more unique ids, you could modify the code.

Edits: Modified the data size and also rewrote the 2nd for-loop.

Upvotes: 1

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