Question

我有一个场景，其中有一个尺寸为N x 1的Label矩阵。标签矩阵中的示例条目如下所示

Label = [1; 3; 5; ....... 6]

我想标签1的随机样本'm1'记录，label2等的'm2'记录，以便输出LabelIndicatorMatrix（N x 1维度）看起来像

LabelIndicatorMatrix = [1; 1; 0;.....1]

1表示已选择记录，0表示在采样期间未选择的记录。输出矩阵满足以下条件

Sum(LabelIndicatorMatrix) = m1+m2...m6

Answer 1

一种可能的解决方案：

Label = randi([1 6], [100 1]);  %# random Nx1 vector of labels
m = [2 3 1 0 1 2];              %# number of records to sample from each category

LabelIndicatorMatrix = false(size(Label));   %# marks selected records
uniqL = unique(Label);                       %# unique labels: 1,2,3,4,5,6
for i=1:numel(uniqL)
    idx = find(Label == uniqL(i));           %# indices where label==k
    ord = randperm(length(idx));             %# random permutation
    ord = ord(1:min(m(i),end));              %# pick first m_k
    LabelIndicatorMatrix( idx(ord) ) = true; %# mark them as selected
end

为了确保我们满足要求，我们检查：

>> sum(LabelIndicatorMatrix) == sum(m)
ans =
     1

以下是我对矢量化解决方案的尝试：

Label = randi([1 6], [100 1]);  %# random Nx1 vector of labels
m = [2 3 1 0 1 2];              %# number of records to sample from each category

%# some helper functions
firstN = @(V,n) V(1:min(n,end));                  %# first n elements from vector
pickN = @(V,n) firstN(V(randperm(length(V))), n); %# pick n elements from vector

%# randomly sample labels, and get indices
idx = bsxfun(@eq, Label, unique(Label)');   %'# idx(:,k) indicates where label==k
[r c] = find(idx);                          %# row/column indices
idx = arrayfun(@(k) pickN(r(c==k),m(k)), 1:size(idx,2), ...
               'UniformOutput',false);      %# sample m(k) from labels==k

%# mark selected records
LabelIndicatorMatrix = false(size(Label));
LabelIndicatorMatrix( vertcat(idx{:}) ) = true;

%# check results are correct
assert( sum(LabelIndicatorMatrix)==sum(m) )

Answer 2

你可以从这个小代码示例开始，它选择标签向量的随机样本，并找到至少选择过一次标签向量的值：

Label = [1; 3; 5; ....... 6];
index = randi(N,m1,1);
index = unique(index);
LabelIndicatorMatrix = zeros(N,1);
LabelIndicatorMatrix(index)=1;

那说我不确定我是否理解LabelIndicatorMatrix的最终条件。

在matlab中对特定行进行采样

2 个答案: