MATLAB。用平均值替换缺失值

Question

问题

如何用字符串（出现次数最多的类）和数字列的平均值替换丢失的列值？

数据示例来自：

UCI ML Repo. Iris

例如，将NaN 替换为'Iris-setosa'

我拥有的代码

它只替换值，但如何替换字符串。

function dataWithReplaced = replaceNaNWithAvg(data)

dataWithReplaced = [ ];

averagePerCol = table2array(varfun(@nanmean, data(: , 1:4)));

for i = 1:4

    dataColumn = table2array(data( : , i));
    dataColumn(isnan(dataColumn)) = averagePerCol(1, i);

    dataWithReplaced = [dataWithReplaced dataColumn];

end

end

我是 MATlab 的新手，很多事情对我来说并不明显。

Answer 1

以下解决方案解决了这个问题：

• 将最后一个表格列转换为元胞数组（保存不同长度的字符串需要元胞数组）。
• Remove all NaN elements from cell array（NaN 元素打断了下一节）。
• Find most repeated string in cell array。
• 在 stringColumn 中查找 NaN 元素的所有索引（我根据上一节使用了 cellfun）。
• 用最常见的字符串替换索引中的元素。

由于您是 Matlab 的新手，我的解决方案对您来说会非常复杂（对我来说看起来很复杂）。
可能有一个更简单的解决方案，我找不到......

参见以下代码示例：

%Create data table for the example.
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
VarName1 = [4.9; 7.3; 6.7; 7.2; 6.5; 6.4; 6.8; 5.7; 5.8; 6.4; 6.5];
VarName2 = [2.5; 2.9; 2.5; 3.6; 3.2; 2.7; 3.0; 2.5; 2.8; 3.2; 3.0];
VarName3 = [4.5; 6.3; 5.8; 6.1; 5.1; 5.3; 5.5; 5.0; 5.1; 5.3; 5.5];
VarName4 = [1.7; 1.8; 1.8; 2.5; 2.0; 1.9; 2.1; 2.0; 2.4; 2.3; 1.8];
VarName5 = {NaN; 'aa'; 'aa'; 'bbb'; NaN; 'ccc'; 'ccc'; 'ccc'; 'ccc'; 'dddd'; 'dddd'};
data = table(VarName1, VarName2, VarName3, VarName4, VarName5);
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

%Convert last table column to cell array.
stringColumn = table2cell(data(:, 5));

%Remove all NaN elements from cell array
%Reference: https://www.mathworks.com/matlabcentral/newsreader/view_thread/314852
x = stringColumn(cell2mat(cellfun(@ischar,stringColumn,'UniformOutput',0)));

%Find most repeated string in cell array:
%Reference: https://www.mathworks.com/matlabcentral/answers/7973-how-to-find-out-which-item-is-mode-of-cell-array
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
y = unique(x);
n = zeros(length(y), 1);
for iy = 1:length(y)
    n(iy) = length(find(strcmp(y{iy}, x)));
end
[~, itemp] = max(n);
commonStr = y(itemp);
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

%Find all indeces of NaN elements in stringColumn.
nanIdx = find(cell2mat(cellfun(@ischar,stringColumn,'UniformOutput',0)) == 0);

%Rplace elements with NaN values with commonStr.
stringColumn(nanIdx) = commonStr;

%Replace last column of original table
data(:, 5) = stringColumn;