randomly select elements of an array

Hi How i can select randomly elements from a matrix o array

I have the matrix and i want to select "x" numbers of elements

thanks

Answer 1

[Walter Roberson]

msize = numel(YourMatrix);
idx = randperm(msize);
YourMatrix(idx(1:x))

If you have a fairly new version of MATLAB, you can instead use

msize = numel(YourMatrix);
YourMatrix(randperm(msize, x))

[Noe alvarado]

thanks. i will try it

[Noe alvarado]

how i can select randomly "N" rows of a matrix?

for example

M =

[ a12, a12]

[ a21, a22]

[ a31, a32]

[ a41, a42]

For N=2

B =

[ a12, a12]

[ a31, a32]

[ a21, a22]

[Sourav Mondal]

>> A=[1 2 3; 4 5 6; 7 8 9]

A =

     1     2     3
     4     5     6
     7     8     9

>> N=2; >> B=A((1:N),:)

B =

     1     2     3
     4     5     6

[bkshn]

Hello Walter Roberson

If I want to find a random element in one row of a matrix, Could you help me How can I do?

For example I want to select a random element in last row of a matrix.

[Walter Roberson]

YourMatrix(end,randperm(size(YourMatrix,2), 1))

[feit feit]

Hi Walter Roberson,

I want to select a random element from a column, for example from Column 1 or Column 2 or Column 3. Would you help me with the code?

Thank you!

[Walter Roberson]

YourMatrix(randi(size(YourMatrix,1)), ColumnNumber)

[feit feit]

Thank you, Walter!

[Jaime Gurrola]

Hi walter, i want to select a random element from this array, help please

A={'Yellow','Green','Blue','Orange','Black','Grey','Red','Brown','Purple','White'};

[Walter Roberson]

A{randi(numel(A))}

Answer 2

[Prasobhkumar P. P.]

histHandle= histfit(data,nBins,'normal');
[Val Ind] = max(histHandle(2).YData);                %histHandle(2) corresponds to the curve fitted
M = histo18(2).XData(Ind);

Answer 3

[Adam Wyatt]

Use "randsample"

For array:

Arry = [1 4 5 7 8 9];
Smpl = randsample(Arry, 3)

Smpl = 1×3

9 5 4

For strings:

Arry = ["Yellow" "Green" "Blue" "Orange" "Black" "Grey" "Red" "Brown" "Purple" "White"];
Smpl = randsample(Arry, 2)

Smpl = 1×2 string array
    "Purple"    "Brown"

How do you want to sample the matrix? If its any element, just convert to array (e.g. Mat(:)). Otherwise you have to apply the function to each row/column separately.

[Walter Roberson]

Note: randsample() is from the Statistics and Machine Learning Toolbox

[Piyush Kant]

Is there any method/parameter with which we can reproduce same random series so that the different algorithms can be evaluated? I know that way it wont be a random series anymore still the psudorandomness can be helpful for multiple runs.

[Steven Lord]

See the "Control Random Number Generation" topic on this documentation page.

Some older functions that use random numbers internally (like eigs, which generates a starting point at random if one is not given to it) have the ability to specify inputs that avoid the randomness (in the case of eigs by specifying v0 in the options structure or specifying the StartVector name-value pair argument.)