how can i select a random number from a column of a matrix? and then how to find the location of that number?

I have a matrix (4x3) and I need to select a value from second column and find the corresponding row number.

For example, A = [11 24 31; 18 19 27; 16 21 34; 23 37 33 28]

Could someone help me?

Answer 1

[Iddo Weiner]

If you use a random number to index the row you want to extract, you will already have what you need:

A = randi(10,[4,3]);
rand_row = randi(size(A,1)) %get random row
rand_number = A(rand_row,2) %get your rand number form the 2nd column

[Rajeev Kant]

it didn't work.

[James Tursa]

Please explain "didn't work" in more detail.

[Steven Lord]

Worked fine for me, Rajeev.

>> A = randi(10,[4,3]);
rand_row = randi(size(A,1)) %get random row
rand_number = A(rand_row,2) %get your rand number form the 2nd column

rand_row =

       4

rand_number =

       6

>> A

A =

       9     7    10
      10     1    10
       2     3     2
      10     6    10

Show us what happened when you tried running those commands. The randi function was introduced in release R2008b, so unless you're running a decade old version of MATLAB you should have it. The rest is basic indexing. As long as you haven't created a variable named size this should work.

[Rajeev Kant]

Thank you guys.

What I am looking for the output will be any random element from the second column i.e. anyone of 24,19,21 and 37 (please discard 28 of the 4th row, apology for typo mistake)

and then the corresponding row number i.e.

for 24, row = 1

for 19, row = 2 and so on.

[Guillaume]

Choosing a random number from the 2nd column and getting the corresponding row is exactly equivalent to choosing a random row and getting the corresponding number in the 2nd column. Iddo showed you how to do the latter, so again you'll have to explain why it didn't work for you.