问题
Let\'s say I have a one-dimensional array:
a = [1, 2, 3];
Is there a built-in Matlab function that takes an array and an integer n
and replicates each
element of the array n times?
For example calling replicate(a, 3)
should return [1,1,1,2,2,2,3,3,3]
.
Note that this is not at all the same as repmat
. I can certainly implement replicate
by doing repmat
on each element and concatenating the result, but I am wondering if there is a built in function that is more efficient.
回答1:
As of R2015a, there is a built-in and documented function to do this, repelem:
repelem
Replicate elements of an array.
W = repelem(V,N)
, with vectorV
and scalarN
, creates a vectorW
where each element ofV
is repeatedN
times.
The second argument can also be a vector of the same length as V
to specify the number of replications for each element. For 2D replication:
B = repelem(A,N1,N2)
No need for kron
or other tricks anymore!
UPDATE: For a performance comparison with other speedy methods, please see the Q&A Repeat copies of array elements: Run-length decoding in MATLAB.
回答2:
I'm a fan of the KRON function:
>> a = 1:3;
>> N = 3;
>> b = kron(a,ones(1,N))
b =
1 1 1 2 2 2 3 3 3
You can also look at this related question (which dealt with replicating elements of 2-D matrices) to see some of the other solutions involving matrix indexing. Here's one such solution (inspired by Edric's answer):
>> b = a(ceil((1:N*numel(a))/N))
b =
1 1 1 2 2 2 3 3 3
回答3:
a = [1 2 3];
N = 3;
b = reshape(repmat(a,N,1), 1, [])
回答4:
>> n=3;
>> a(floor((0:size(a,2)*n-1)/n)+1)
ans =
1 1 1 2 2 2 3 3 3
回答5:
Some exotic alternatives. Admittedly more funny than useful:
Assign the (first) result of
meshgrid
to a vector:b = NaN(1,numel(a)*n); %// pre-shape result b(:) = meshgrid(a,1:n);
Build a matrix that multiplied by
a
gives the result:b = a * fliplr(sortrows(repmat(eye(numel(a)),n,1))).';
Use
ind2sub
to generate the indices:[~, ind] = ind2sub([n 1],1:numel(a)*n); b = a(ind);
回答6:
If you have the image processing toolbox, there is another alternative:
N = 3;
imresize(a, [1 N*numel(a)],'nearest')
回答7:
% To get b = [1 1 1 2 2 2 3 3 3]
N = 3;
a = [1 2 3];
temp_a = a(ones(N,1),:);
b = reshape(temp_a,1,numel(temp_a));
% To get b = [1 2 3 1 2 3 1 2 3]
N = 3;
a = [1 2 3];
temp_a = a(ones(N,1),:);
b = reshape(temp_a',1,numel(temp_a));
来源:https://stackoverflow.com/questions/1947889/element-wise-array-replication-in-matlab