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'How to' Matrix

Asked by Hello kity

Hello kity

on 12 Dec 2012

I have an array with 0 s and 1s.

Example a colomn, 0 ,0 ,0 ,0 , 1.

Now the 1 is on the 5th row, I want to raise that to the first row.

So, in my code i want all the ones to go 4 steps up...

sounds easy, but how :) ?

5 Comments

Jan Simon

Jan Simon

on 12 Dec 2012

@Student: The question remains, what "raise to the first row" exactly means. At first I guess it is the "first column", but "raising" can be swapping, shifting, circular shifting, sorting, cropping or any procedure I cannot imagine currently.

Hello kity

Hello kity

on 12 Dec 2012

I meant shifting, shifting the 1 on the 4th row to the 1st.

Jan Simon

Jan Simon

on 12 Dec 2012

Thanks for the clarification, Student. And what happens on the right margin? Is the result shorter, filled with zeros or ones or with the value of the last element?

Hello kity

Hello kity

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4 Answers

Answer by Walter Roberson

Walter Roberson

on 12 Dec 2012
Edited by Walter Roberson

Walter Roberson

on 12 Dec 2012

Have you considered circshift() up by 4 rows?

0 Comments

Walter Roberson

Walter Roberson

Answer by Azzi Abdelmalek

Azzi Abdelmalek

on 12 Dec 2012
A=[0 0 0 0 0 1 0 0 0 0 0 1 0 0 0 1]
for k=5:length(A)
   if A(k)
       b=A(k-4:k-1);
       A(k-4)=1
       A(k-4+1:k)=b
   end
end

2 Comments

Hello kity

Hello kity

on 12 Dec 2012

Would you comment this code step by step, I dont get how you do this...

thank you

Azzi Abdelmalek

Azzi Abdelmalek

on 12 Dec 2012
 A=[0 0 0 0 0 1 0 0 0 0 0 1 0 0 0 1]
for k=5:length(A)
   if A(k)            % If A(k) is equal to 1
       b=A(k-4:k-1);  % store value from k-4 to k-1 in b
       A(k-4)=1       % replace value at k-1 by 1
       A(k-4+1:k)=b   % shift value stored in b 
   end
end
Azzi Abdelmalek

Azzi Abdelmalek

Answer by Andrei Bobrov

Andrei Bobrov

on 12 Dec 2012
Edited by Andrei Bobrov

Andrei Bobrov

on 12 Dec 2012

other way:

a - your vector - row (eg: [0 0 0 0 1])

n = numel(a);
out = a(hankel(1:n,[n,1:n-1]));

or

out = hankel(a,circshift(a,[0 1]));

1 Comment

Hello kity

Hello kity

on 12 Dec 2012

thank you,

afterwards i use Q=out(:,5);

Andrei Bobrov

Andrei Bobrov

Answer by Jan Simon

Jan Simon

on 12 Dec 2012
Edited by Jan Simon

Jan Simon

on 12 Dec 2012

Some ideas:

x = [0, 0, 0, 0, 1];
index = find(x, 1, 'first');
y1 = x(index:end);
y2 = [x(index:end), zeros(1, index - 1)];
y3 = [x(index:end), ones(1, index - 1)];
y4 = [x(index:end), repmat(x(end), 1, index - 1)];
y5 = [x(index:end), x(1:index - 1)];

0 Comments

Jan Simon

Jan Simon

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