getting first 20% of a matrix

I am getting the first 20% of a (290,2) matrix (so a 58,2 matrix). I was just wondering how this is possible. im presuming there are a number of ways but unsure as to how to do it?

[Stephen23]

What do you mean by the "first 20% of a matrix" ?

• The first 20% of the rows, starting from the first row?
• the first 20% of the columns, starting from the first column?
• the first 20% of the elements, starting from the first element?
• the first 20% of the values, when the values are sorted by value?
• something else?

Answer 1

[Guillaume]

Just use standard matrix indexing:

A = rand(290, 2); %for example;

B = A(1:floor(size(A, 1) * 0.2), :);