Thread Subject: i need some help

hello, is there anyway to find how many times an integer appears in a vector?

for example i have the vector [1 2 3 3 4 4 5 5]

and the answer should be [1 2 9 16 25]
when the number next to another is the same they multiply together

any hints?

It seems like you are asking two different questions. For the second one, you could do:


A = [1 2 3 3 4 4 5 5]; % Given vector
B = ~[1 diff(A)];
A(B) = A(B).^2;
A(circshift(B,[0 -1])) = []

"andreas " <thryloss2003@msn.com> wrote in message <gg21ke$3hi$1@fred.mathworks.com>...
> hello, is there anyway to find how many times an integer appears in a vector?
>
> for example i have the vector [1 2 3 3 4 4 5 5]
>
> and the answer should be [1 2 9 16 25]
> when the number next to another is the same they multiply together
>
> any hints?

% The question you asked is not the answer you are seeking.
% Do this integers always increase? (Is [ 1 2 3 3 2 1] allowed?)
% But, for hints try:

doc unique
doc diff
doc histc
doc sort

% That should get you started.

"Matt Fig" <spamanon@yahoo.com> wrote in message <gg24kh$c5f$1@fred.mathworks.com>...
> It seems like you are asking two different questions. For the second one, you could do:
>
>
> A = [1 2 3 3 4 4 5 5]; % Given vector
> B = ~[1 diff(A)];
> A(B) = A(B).^2;
> A(circshift(B,[0 -1])) = []

yeah but the problem is that the program must do the multiplication also if three and more numbers are placed in the vector
for example [ 1 2 2 2 3 3 3 4 4 4]
should give [1 8 27 64]

> yeah but the problem is that the program must do the multiplication also if three and more numbers are placed in the vector
> for example [ 1 2 2 2 3 3 3 4 4 4]
> should give [1 8 27 64]

If your vectors are always sorted like this then you can use:

A = [ 1 2 2 2 3 3 3 4 4 4];
B = accumarray(A', A,[length(A),1],@prod,NaN);
B(isnan(B))=[]

actually the question is this :

Write a Matlab function, named prodrep, that given a vector of numbers, computes the product of repeating
values in the vector. You should check the input is a vector and that it contain numbers. An example
result generated by your function might be:
>> vec = [1 2 2 2 3 3 2 2 2 2 1 1];
>> prodrep(vec)
ans =
1 8 9 16 1
For the example above, the first element is 1 (this value doesn’t repeat), the second element is given by
2  2  2, the third element by 3  3, the fourth by 2  2  2  2, and the last by 1  1. Similarly:
>> vec = [5 6 3 3 4 4 4 5 5 5 5 6 6 7];
>> prodrep(vec)
ans =
5 6 9 64 625 36 7

just think about it!!!!=)

A = [ 6 6 1 2 2 2 5 5 5 1 4 4 4 4 4 2 2];
tmp = [1 diff(A)]~=0;
V = A(tmp).^diff(find([tmp 1]));

"Matt Fig" <spamanon@yahoo.com> wrote in message <gg2ff0$9er$1@fred.mathworks.com>...
> A = [ 6 6 1 2 2 2 5 5 5 1 4 4 4 4 4 2 2];
> tmp = [1 diff(A)]~=0;
> V = A(tmp).^diff(find([tmp 1]));

thanx very much, but can you explain to me each one of the lines to understand what it's done by the program?;p

> tmp = [1 diff(A)]~=0;
> V = A(tmp).^diff(find([tmp 1]));

these two lines please...if you can

> thanx very much, but can you explain to me each one of the lines to understand what it's done by the program?;p
>
> > tmp = [1 diff(A)]~=0;
> > V = A(tmp).^diff(find([tmp 1]));

I can, but you have to learn something from this exercise! Just take apart what I wrote and look at each component, using the help for diff and find if necessary.