How to find the position of a number in an array?

I have a column vector Y which is 7306409x1 double. I want to find the position (indices) of a specifric number (8) in Y. I used

k=find(Y==8)

But MATLAB gives the answer

k =

0×1 empty double column vector

and does not show the indices. I think the problem is something with the "double". Does anyone know how to solve this?

Thanks!

[madhan ravi]

Is Y integer or double?

Answer 1

[Matt J]

There is nothing wrong with your code as long as there are elements in Y that are exactly equal to 8

>> Y=[8 1 2 5 8 6];
>> k=find(Y==8)

k =

     1     5

Suprises may happen, however, if Y contains floating point inaccuracies that you can't see on the screen,

>> Y=[8 1 2 5 8 6] + 10*eps,

Y =

    8.0000    1.0000    2.0000    5.0000    8.0000    6.0000

>> k=find(Y==8)

k =

  1×0 empty double row vector

One solution is to round,

  >> k=find(round(Y)==8)

k =

     1     5

[CS]

Thanks!

Sounds like MATLAB rounds the numbers up.

When we click on a variable in the Workspace window, it will be shown in the Varibles window; however, MATLAB rounds up the number; 19.993690 for instance, will be shown by 19.9937.

I had one data file A and I opened the Y In Variable window and recorded the value shown as 19.9937. I wanted to find the position of this value in data file B.

So, I opened data file B and called find(Y==19.9937). But, because the exact value has been 19.993690, MATLAB gave me the error as 1×0 empty double row vector.

Do you know how I can see the long format of numbers in the Variable window?

[madhan ravi]

format longg

[CS]

format long will show the long format of numbers in the command window. My question is regarding to how show the long format of numbers in the Variables window?

[Matt J]

My question is regarding to how show the long format of numbers in the Variables window?

That can be adjusted in the view tab

However, rather than relying on copy-paste, I think it would be better to simply do,

k=find(Y==Y(283))

Answer 2

[madhan ravi]

k = find( (abs(Y) - 8) < 1e-2 ) % where 1e-2 is the tolerance