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'How to' Matrix

Asked by 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 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 on 12 Dec 2012

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

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

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4 Answers

Answer by Walter Roberson on 12 Dec 2012
Edited by Walter Roberson on 12 Dec 2012

Have you considered circshift() up by 4 rows?

0 Comments

Walter Roberson
Answer by 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 on 12 Dec 2012

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

thank you

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
Answer by Andrei Bobrov on 12 Dec 2012
Edited by 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 on 12 Dec 2012

thank you,

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

Andrei Bobrov
Answer by Jan Simon on 12 Dec 2012
Edited by 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

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