random selection of a cell

Hello,

I have a cell(matrix) of size 100*100.I need to scan each column and choose 4 consecutive random cells( (1*1)*4) for assigning values.Can anyone please help me with this?

Thanks in advance

[madhan ravi]

A short example?

[KK14]

I have a 100*100matrix. Suppose I take x as my random value & column say 'y'.So my selection among the 100 elements in the column should be (x:x+4, y)

ex: if x = 7, y =4

selection = (7:10, 4)

Answer 1

[KSSV]

You got 100 columns.....you can pick any one element/ position out of it randomly using randperm.

% loop for each column
for i = 1:100
    % pick element randomly 
    p = randperm(100,1) ; 
end

[KK14]

This would give me just 1 cell,but I need 4

[KSSV]

You said you want continuously right? Then simply taken next four from them.

% loop for each column
for i = 1:100
    % pick element randomly 
    p = randperm(100,1) ;
    if p > 96
        p = 96 ; 
    end
    idx = p:p+4 ; 
end

[KK14]

Thankyou for the answer.Idea works just fine.

Answer 2

[Bruno Luong]

A = zeros(100,100);
something = 1;
for c = 1:100
    r = randi(97) + (0:3);
    A(r,c) = something;
end

[KK14]

In my case 97 wouldn't work.I do not always have 100 rows(question was generally asked).It would throw an error if I put randi (A(end))+(0:3) (A here is my array,say).

[Bruno Luong]

Replace "r = randi(97) ..." by

ncons = 4;
r = randi(size(A,1)-ncons+1)+(0:ncons-1) 

You also specify 4 consecutive rows in your original question. Feel free if you want change 4 to something else.

[KK14]

Thankyou for the answer.Had to modify, but the idea helped.