跨行计算孤岛中出现的次数 - MATLAB

Question

我需要以下函数的帮助：for 循环或向量化代码中的 histc 和 numel。我有一个可以是任何维度的矩阵。代码需要输出一个元素在一个区间内出现的次数，直到每一行的末尾。因此对于下面的示例，我想找出第 1 行中数字 1 出现的次数。因此在第 1 行中，数字 1 在被两个 0 打断之前出现了两次。然后它再次出现在最后一列中。所以输出将是 2 1。

感谢您的帮助。谢谢

x = hist( data, numel(unique(data)) );
y = histc( data, unique(data) );

data (input) 5x5

1   1   0   0   1
1   1       1   1
0           0   1
0   0   1   1   1
1   0   1   1   1

y (output) 

2 1
2 2
1
3
1 3

Answer 1

假设 x 是输入数组，这可能是一种方法 -

[nrows,ncols] = size(x);
new_ncols = ncols + 2;

%// Pad one column of zeros on left and right sides of x
x_pz = [zeros(nrows,1) x zeros(nrows,1)] 

%// Flatten padded x
x_pzf = reshape(x_pz',[],1)'

%// Start & end indices of islands of ones for flattened padded x
starts = strfind(x_pzf,[1 0]);
ends = strfind(x_pzf,[0 1])

row_ids = ceil(starts/new_ncols); %// row IDs for  each island of ones

%// Start & end indices of islands of ones for flattened non-padded (corrected) x
starts_cor = ends - 2*(row_ids-1)
ends_cor = starts - (2*row_ids-1)

%// Get number of elements in each island of ones 
counts = ends_cor - starts_cor + 1

%// Bin row_ids for each row of input array
counts_per_row = histc(row_ids,1:nrows)

%// Now setup output array with conts for each island corresponding to each
%// row ending up in its each row and setting the blank spaces as NaNs
mask = bsxfun(@ge,counts_per_row,(1:max(counts_per_row))') %//'
y = NaN(size(mask))
y(mask) = counts
y = y'

代码运行-

>> x (modified from the original one to test out more varied situations)
x =
     1     1     0     0     1     1
     1     1     0     1     1     0
     0     0     0     0     1     0
     0     0     1     1     1     0
     1     0     1     1     1     1
     1     1     1     1     1     1
     0     0     0     0     0     0
     0     1     0     1     0     1
>> y
y =
     2     2   NaN
     2     2   NaN
     1   NaN   NaN
     3   NaN   NaN
     1     4   NaN
     6   NaN   NaN
   NaN   NaN   NaN
     1     1     1

如果您正在寻找一种更直观、更简洁的方式来获取和显示最终输出，您可以使用元胞数组。所以，你可以这样做 -

>> ycell = arrayfun(@(n) counts(row_ids==n),1:nrows,'Uni',0);
>> celldisp(ycell)
ycell{1} =
     2     2
ycell{2} =
     2     2
ycell{3} =
     1
ycell{4} =
     3
ycell{5} =
     1     4
ycell{6} =
     6
ycell{7} =
     []
ycell{8} =
     1     1     1

跨行计算孤岛中出现的次数 - MATLAB

Count occurrences of ones in islands across rows - MATLAB

matlab

for-loop

vectorization