I'm a newbie for eigen library. Here is a silly question, which I could not find the answer from the doc.
Is there an way to access a subset of entries of vector or matrix using indicator or index like matlab? For example, for such an expression
x(x>0)=0;
how can I do it in eigen without using for loop?
Thanks

I need the same functionality like you.
I don't have an expression, but a vector containing indices. And then I would like to compose a new matrix containing the rows taken at the indices from another big matrix.

something like this:

Code: Select all

VectorXf idx = something.row(i);
MatrixXf ordered = ??; //othermatrix(idx,:) in Matlab


Have you found out something already? I searched the doc for something like a filter to be applied on a matrix or a way to access multiple rows/columns but have not found anything usefull. I think in the meanwhile I have to copy it manually in a loop.

Ismael

sth4nth wrote:I'm a newbie for eigen library. Here is a silly question, which I could not find the answer from the doc.
Is there an way to access a subset of entries of vector or matrix using indicator or index like matlab? For example, for such an expression
x(x>0)=0;
how can I do it in eigen without using for loop?
Thanks

Like this (here x is a MatrixXf of size n-by-p):

(x.array() >= 0.f).select(x, MatrixXf::Zero(n,p));

IsmaelNetzel wrote:I need the same functionality like you.
I don't have an expression, but a vector containing indices. And then I would like to compose a new matrix containing the rows taken at the indices from another big matrix.

something like this:

Code: Select all

VectorXf idx = something.row(i);
MatrixXf ordered = ??; //othermatrix(idx,:) in Matlab


Have you found out something already? I searched the doc for something like a filter to be applied on a matrix or a way to access multiple rows/columns but have not found anything usefull. I think in the meanwhile I have to copy it manually in a loop.

Ismael

We don't currently have this feature but it's been asked for many times and even discussed on the mailing list...