[英]Replacing values closest to Nan with a value, within a matrix, in Matlab
I am new to Matlab and I have a matrix: 我是Matlab的新手,我有一个矩阵:
M =[NaN NaN NaN 2010 5454;
NaN NaN 2009 3000 5000
NaN 2011 3256 5454 6000
2009 4000 5666 6545 5555
5000 5666 6000 7000 8000];
I want to replace values closest to Nan with a value of 2010. I know how to do it manually and one by one. 我想将最接近Nan的值替换为2010年的值。我知道如何手动进行操作,并且一步一步地进行操作。 Is there any to create a loop to find these values and replace them? 是否可以创建一个循环来查找这些值并替换它们? The result should look like this: 结果应如下所示:
M =[NaN NaN NaN 2010 5454;
NaN NaN 2010 3000 5000
NaN 2010 3256 5454 6000
2010 4000 5666 6545 5555
5000 5666 6000 7000 8000];
Thank you in advance. 先感谢您。
Thanks to @crazyGamer for improving the answer with explanations and clearer variable names. 感谢@crazyGamer通过解释和更清晰的变量名来改善答案。
You can use 2D-convolution to detect entries that are close to a NaN
; 您可以使用2D卷积来检测接近NaN
条目; select non- NaN
's among those entries, and write the desired value there. 在这些条目中选择非NaN
,然后在其中写入所需的值。
Closeness is defined by means of a neighbourhood binary mask. 紧密度通过邻域二进制掩码定义。 This usually has 4
neighbours (up, down, left, right) or 8
(including diagonals). 通常有4
邻居(上,下,左,右)或8
(包括对角线)。
The code is generalized to use either mask as per choice. 该代码被通用为根据选择使用任一掩码。
% Data:
M = [ NaN NaN NaN 2010 5454;
NaN NaN 2009 3000 5000;
NaN 2011 3256 5454 6000;
2009 4000 5666 6545 5555;
5000 5666 6000 7000 8000 ];
neighbourhood = [0 1 0; 1 0 1; 0 1 0];
% or [1 1 1; 1 0 1; 1 1 1] for 8-neighbours
new_value = 2010;
% Computations:
nanInds = isnan(M);
nanIndsWithNeighs = conv2(nanInds, neighbourhood, 'same')~=0;
neighInds = ~nanInds & nanIndsWithNeighs; % logical AND
M(neighInds) = new_value;
It is possible without defining any explicit loops. 无需定义任何显式循环是可能的。 Below are the steps and sample code. 下面是步骤和示例代码。
find
function to determine which elements are NaN
. 使用find
函数确定哪些元素为NaN
。 % Row and column indices of NaN in array `a`
[x, y] = find(isnan(a));
% All 4-neighbor elements around each NaN
r = [x-1 x+1 x x];
c = [y y y-1 y+1];
% Delete those values that are outside the array bounds
% (For NaNs in the edges)
outInd = r < 1 | r > size(a, 1) | c < 1 | c > size(a, 2);
r(outInd) = [];
c(outInd) = [];
% Replace all these neighbors with required value
a(sub2ind(size(a), r, c)) = 2010;
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