How to create a new vector from another vector which contains the value times the index

Hello, I'm new to programming and I would like to create a new vector2 from another vector1 which contains i*vector1(i).

Let's say I have

vector1 = [5,4,3,1]

So vector2 should look like this: vector2 = [1,1,1,1,1,2,2,2,2,3,3,3,4]

I tried to use a nested for-loop but I can't get the result right.

vector1 = [5,4,3,1]
vector2 = []
for i = 1:length(vector1)
    for j = 1:vector1(i)
    Vektor2 = [j*i]
    end
end

I would be thankfull for any suggestions.

[Stephen23]

v1 = [5,4,3,1];
v2 = repelem(1:numel(v1),v1)

v2 = 1×13

1 1 1 1 1 2 2 2 2 3 3 3 4

[Radde1683]

Works well too, thank you!

[Romechelle]

p=[1 2 3 4 5 6 7 8 9 10 -1 -2]
q=[4 1 3 -2 1 -8 4 -11 9 6 13 -4]

create a new row vector s that is made of the elements of p that are less than or equal to the corresponding elements of q

[Jan]

@Romechelle: Please do not post a new question in the section for comments of another question. Open a new thread instead and delete this comment. Thanks.

Answer 1

[Jan]

v1 = [5,4,3,1];
v2 = [];
for i = 1:length(v1)
    for j = 1:v1(i)
       v2 = [v2, i];
    end
end

You can omit the inner loop for more matlab'ish code:

v2 = [];
for i = 1:length(v1)
   v2 = [v2, repmat(i, 1, v1(i))];
end

An efficient method would be:

vector2 = repelem(1:numel(vector1), vector1)

or in old Matlab versions before repelem was introduced:

v1  = [5,4,3,1];
ind = zeros(1, sum(v1));
ind(cumsum([1, v1(1:end-1)])) = 1;
v2 = cumsum(ind)

[Radde1683]

Thank you really much!

[Jan]

You are welcome. I know, that it is not useful to solve otherones homework. But if you understand the 3 different approachs, you have learned something important about Matlab also.