how i will choose a random element of a matrix and then find in which row,column it is

6 次查看（过去 30 天）
Giannakis Stoukas
Giannakis Stoukas 2015-3-31
编辑： Stephen23 2015-4-1
I have a matrix A and i want to insert to a variable a random element of this matrix,except two numbers 0 and 1.Then i want to find in which row/column the element is

请先登录，再回答此问题。

回答（3 个）

Image Analyst
Image Analyst 2015-3-31
You can use randperm() to get a random location. Get one location to extract the random element of A, and another location to get the location where you want to insert that random element. I don't know what "except two numbers 0 and 1" means - please clarify. To find where a certain integer lives in A, use find
[rows, columns] = find(A == yourDesiredNumber);
  2 个评论
Giannakis Stoukas
Giannakis Stoukas 2015-3-31
I mean that the variable mustnot take the element that has value 0,or 1.For example,if i have a matrix A=[ 2 3 1;8 7 6; 5 4 0] the variable can take the value of a random element of the matrxix,excluding the 1 and zero,but it can take the value 2,3,8,7,6,5,4 one of them
Image Analyst
Image Analyst 2015-3-31
Try code like this:
loopCounter = 0; % Failsafe.
maxTries = 100000
while loopCounter < maxTries
randomElement = A(randomRow, randomColumn)
if randomElement <> 0 && randomElement <> 1
% Success! We found a good element. Quit looking now.
break;
end
loopCounter = loopCounter + 1;
end
if loopCounter == 0
message = sprintf('No non-0 or non-1 elements found after %d tries.',...
loopCounter);
uiwait(warndlg(message));
end

请先登录，再进行评论。

Jon
Jon 2015-3-31
I think something like this would work.
is01 = true; initialize flag for while loop
while is01
ind=randi(numel(A)); % Pick the random element
is01 = ismember(A(val),[0 1]); % see if selected element is 0 or 1
end
[row,col]=ind2sub(size(A),ind); % get the row and column of the selected element
val=A(ind); % or A(row,col), store the value of the random element in val
If the selected element is 0 or 1, is01 will stay true and the loop will continue. If the selected element is not 0 or 1, is01 will become false and the loop will terminate with the index of the random element stored in ind and its value in val. The ind2sub command converts the index to a row and column reference.
Stephen23
Stephen23 2015-3-31
编辑：Stephen23 2015-4-1
Instead of using slow loops this can be achieved using fully vectorized code, by only generating the required indices:
>> A = [2,3,1;8,7,6;5,4,0];
>> B = find(A>1);
>> X = randi(numel(B));
>> A(B(X))
ans =
5
>> [r,c] = ind2sub(size(A),B(X))
r =
3
c =
1
This code is much faster than using loops, and makes changing the exclusion condition very easy. It also makes it easy to randomly select multiple elements (not just one) by providing the optional size input to randi:
>> X = randi(numel(B),[1,23]);
>> A(B(X).')
ans =
7 3 6 8 5 2 6 7 3 7 3 7 3 4 3 6 8 2 2 2 5 3 5
>>[r,c] = ind2sub(size(A),B(X).')
r =
2 1 2 2 3 1 2 2 1 2 1 2 1 3 1 2 2 1 1 1 3 1 3
c =
2 2 3 1 1 1 3 2 2 2 2 2 2 2 2 3 1 1 1 1 1 2 1
Note that zero and one do not appear in the output matrix! The transpose is optional.

类别

在 Help Center 和 File Exchange 中查找有关 Creating and Concatenating Matrices 的更多信息

标签

Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!

Translated by