Split data into different arrays of different sizes?

Hi I have a huge vector of data and I would like to divide it into different groups according to a particular index so lets say my data is a= (1 2 3 4 5 6 7 8....) and my index is i= (1,2,3,4..) which sum is equal to the size of a. How can I split "a" vector according to the index "i"?

Answer 1

[KSSV]

If a is the vector and index is i.

iwant = a(i)

[pauldjn]

Thanks but that only shortened my vector I want to group them in columns of specified elements according to the index

[KSSV]

How your indices are given?

[pauldjn]

Is a vector i = (1 2 3 4 5 6...) etc

Answer 2

[Stephen23]

accumarray(index(:),a(:),[],@(v){v})

[pauldjn]

I got this error message: Second input VAL must be a vector with one element for each row in SUBS, or a scalar.