Matlab：如何在每n行中插入'NaN'

Question

这只是一个非常简单的例子来说明我的问题。

a=ones(5)  

如何在每两行之后插入NaN:

我知道做这个简单例子的方法是:

b(:,1:5)=NaN
[a(1:2,:);b;a(3:4,:);b;a(end,:)]

但问题是，如果矩阵是60000 × 200(可能更大)，那么我如何在每两行之后插入' NaN '。

非常感谢。

Answer 1

a = ones(5); %// example data
n = 2; %// number of rows
N = floor(size(a,1)*(1+1/n)); %// final number of rows
ind = mod(1:N, n+1) ~= 0; %// logical index for non-NaN rows
b = NaN(N,size(a,2)); %// initiallize result to NaN
b(ind,:) = a; %// fill in non-NaN rows

Answer 2

我想不出一个简单的单行解决方案。这可以在一个非常紧密的循环中完成。

a = ones(5);
a_with_nans = nan(floor(size(a,1)*(3/2)), size(a,2)); %Start with all nans in a larger matrix
for ix = 1:2:size(a,1)
    a_with_nans(ix*3/2-(1/2),:) = a(ix,:);
    if ix+1<=size(a,1)
        a_with_nans(ix*3/2-(1/2)+1,:) = a(ix+1,:);
    end
end

:

a_with_nans =
     1     1     1     1     1
     1     1     1     1     1
   NaN   NaN   NaN   NaN   NaN
     1     1     1     1     1
     1     1     1     1     1
   NaN   NaN   NaN   NaN   NaN
     1     1     1     1     1

Answer 3

你可以这样做:

>> a= [ 1 2 3 4 5 6 7 8 9]
a =
     1     2     3     4     5     6     7     8     9
>> b = nan(floor(length(a)/2),1)'
b =
   NaN   NaN   NaN   NaN
>> a_new = zeros(1, length(a)+length(b))
a_new =
     0     0     0     0     0     0     0     0     0     0     0     0     0
>> b_i = 3:2:length(a)
b_i =
     3     5     7     9
>> a_new(b_i+(0:length(b_i)-1)) = b
a_new =
     0     0   NaN     0     0   NaN     0     0   NaN     0     0   NaN     0
>> a_new(~isnan(a_new))=a
a_new =
     1     2   NaN     3     4   NaN     5     6   NaN     7     8   NaN     9