Replacing values in a matrix based on values in a column vector

3 vues (au cours des 30 derniers jours)
I have a column vector (with dimensions m x 1) which contains values from 1 to 10.
I want to make a matrix yMat with dimension m x 10, such that, in corresponding rows of y and yMat, the value at the column of yMat corresponding to the value in y is equal to 1.
All other values in yMat should be 0.
For example, if
y = [2; 4; 1; 8]
then
yMat = [0 1 0 0 0 0 0 0 0 0; 0 0 0 1 0 0 0 0 0 0; 1 0 0 0 0 0 0 0 0 0; 0 0 0 0 0 0 0 1 0 0]
The following code works, but is there any way to do this without using a for loop?
yMat = zeros(m, 10); % m is the number of rows in column vector y
for i = 1:m
yMat(i, y(i)) = 1;
end

Réponse acceptée

Digaamber Dhamija
Digaamber Dhamija le 22 Juin 2020
Modifié(e) : Digaamber Dhamija le 22 Juin 2020
Just in case anyone else has a similar problem, I found an even simpler solution.
y = [2; 4; 1; 8];
yMat = 1:10 == y;
which produces a logical array yMat.
You can get numeric values by doing:
yMat = double(1:10 == y);
producing
yMat =
0 1 0 0 0 0 0 0 0 0
0 0 0 1 0 0 0 0 0 0
1 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 1 0 0

Plus de réponses (1)

Mara
Mara le 21 Juin 2020
I came up with this. But not sure if this the easiest way to do it.
yMat = zeros(length(y)*10, 1);
yMat((y-1)*length(y)+ (1:length(y))') =1;
yMat = reshape(yMat, length(y), []);
  2 commentaires
Digaamber Dhamija
Digaamber Dhamija le 21 Juin 2020
Modifié(e) : Digaamber Dhamija le 21 Juin 2020
The formula
(y-1)*length(y) + (1:length(y))'
seems to be doing something similar to calculating the linear indices for the original dimensions of yMat.
It would also have worked if you did this
yMat = zeros(length(y), 10);
yMat((y-1)*length(y) + (1:length(y))') = 1;
Mara
Mara le 21 Juin 2020
True, it does not have to be a vector for the indexing to work. Thanks for the feedback! I did not see that you received another answer already, it seems to be more intuitive than this one, anyways.

Connectez-vous pour commenter.

Catégories

En savoir plus sur Creating and Concatenating Matrices dans Help Center et File Exchange

Produits


Version

R2020a

Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!

Translated by