使用基于索引 MATLAB 的元素填充元胞数组

Question

我有一个 n*m 元胞数组 Cell_In:

a b
* *
* *
c *
* d
* *
* f

* --> 表示空字符串（''）。这是我需要的：

a b
a b
a b
c b
c d
c d
c f

对于特定列，我需要用前一个非空单元格填充空单元格，直到找到另一个非空单元格。以下是我写的代码。

b = ~cellfun(@isempty,a);
c = [find(b(:,1) == 1);size(a,1)+1]; e = diff(c);
d = [find(b(:,2) == 1);size(a,1)+1]; f = diff(d);
s1 = ''; s2 = '';
for i = 1:length(e)
    s1 = [s1,repmat(a(c(i),1),1,e(i))];
end

for i = 1:length(f)
    s2 = [s2,repmat(a(d(i),2),1,f(i))];
end
Cell_Out = [s1',s2'];

它运行良好，但我想知道最佳解决方案？

Answer 1

假设 A 是输入元胞数组，这里可能有两种方法。

方法 #1

%// Initlialize output array
Aout = cell(size(A));

for k = 1:size(A,2)

    %// Select one column
    Ak = A(:,k);

    %// Logical array with size of Ak and ones at places with non-empty strings
    pos = cellfun(@(x) ~isempty(x), Ak);

    %// Find unique strings and find indices for all places in that column
    %// with respect to those unique strings
    [unq_str,~,str_idx] = unique(Ak,'stable');

    %// Perform cumsum on pos to get an array with a "stepped" array that
    %// steps up at each non-empty string position.
    %// Then replace each stepping number with the string IDs
    idx = changem(cumsum(pos),str_idx(pos),1:sum(pos));

    %// Index into each column with those replaced IDs for the final output
    Aout(:,k) = unq_str(idx);
end

为了更积极地测试解决方案代码，稍微改变了输入，我们得到了代码运行 -

A = 
    'a'    'b'
    ''     '' 
    ''     'a'
    'c'    '' 
    ''     'd'
    'a'    '' 
    ''     'f'
    'c'    'a'

Aout = 
    'a'    'b'
    'a'    'b'
    'a'    'a'
    'c'    'a'
    'c'    'd'
    'a'    'd'
    'a'    'f'
    'c'    'a'

方法 #2 [紧凑且可能更高效]

您可以将输入元胞数组重新整形为单列元胞数组，这样您就不需要遍历元胞数组，这可能会导致更高效和紧凑的代码 -

%// Reshape all cells into a single columned cell array
A1 = A(:);

%// Rest of the code borrowed from previous approach with reshaping added
%// at the end to bring the output back to the size of input array
pos = ~cellfun('isempty', A1);
[unq_str,~,str_idx] = unique(A1,'stable');
Aout =  reshape(unq_str(changem(cumsum(pos),str_idx(pos),1:sum(pos))),size(A));

奖励：changem

的自定义实现

前面列出的代码使用changem that needs Mapping Toolbox. So, if you do have it, here's a customized version of it, implemented with bsxfun and max and is merely a polished version of an earlier solution code posted here。这是自定义函数代码 -

%// CHANGEM_CUSTOM  Home-cooked vesion of CHANGEM with MAX, BSXFUN
function A  = changem_custom(A,newvals,oldvals)

[valid,id] = max(bsxfun(@eq,A(:),oldvals(:).'),[],2); %//'
A(valid) = newvals(id(valid));

return;

因此，要使用此自定义函数来替换 changem，只需替换前面代码中的函数调用名称即可。

Answer 2

此解决方案获取空单元格的索引并用前一个单元格的数据填充它。要填补更大的空白，需要多个步骤。

ix=find(cellfun(@isempty,M))
while numel(ix)>0, M(ix)=M(ix-1);ix=find(cellfun(@isempty,M)); end

使用基于索引 MATLAB 的元素填充元胞数组

Fill cell array with elements based on the indices MATLAB

matlab

cell-array