Delete first n rows in column vector in Matlab & call array rows by an array of indices

Question

I have 2 questions.

Question 1:

I have a column vector, v, with (say) 1000 rows. I want to delete first (say) n rows (for example n=300 to remove the first 300 rows of v).

Question 2:

I have an array of indices. How can it be used to get rows of another array whose index values are in first array?

I = [ 1 2 4 5] %// array of indices

Q = [ 45 22 66 87 99 10 ] %// input array 

Desired Output:

O = [45 22 87 99] %// output array

Answer 1

For you first question:

N=300;
v=rand(1000,1); %// sample data
v(1:N)=[];

And the second:

O=Q(I)