Find index of a number in a 3d array

Hi.

I have a 14610x146x220 3d array. I know that somewhere in this array there is a value of 31.5814 however i dont know what is the index of this value. May i know how do i find out what is the index of this value?

Edit:

For me I used the solution from

https://www.mathworks.com/matlabcentral/answers/1804400-find-index-of-a-number-in-a-3d-array#comment_2361320

Thanks all for helping.

Answer 1

[Torsten]

i = find(A(:) == 31.5814);
[i1 i2 i3] = ind2sub([14610,146,220],i(1));
A(i1,i2,i3)

But most probably, floating point inaccuracies will inhit finding the value.

You could try

epsilon = 1e-6;
i = find(abs(A(:)-31.5814)<epsilon);
[i1 i2 i3] = ind2sub([14610,146,220],i(1));
A(i1,i2,i3)

[Baiwen Ding]

Hi. I have tried both methods but they didnt work. It says "Index exceeds the number of array elements. Index must not exceed 0."

[Torsten]

Works for me.

Of course, instead of A, you will have to use the name of your array.

A = rand(3,5,2);
A(2,2,1) = 1.0;
epsilon = 1e-6;
i = find(abs(A(:)-1.0)<epsilon);
[i1 i2 i3] = ind2sub(size(A),i(1))

i1 = 2

i2 = 2

i3 = 1

A(i1,i2,i3)

ans = 1

[Baiwen Ding]

Hi thanks for the friendly reminder.

Lets call my data, the 14610 x 146 x 220 3d array, "Temp".

I think I found the issue. Even though the size of both rand(14610,146,220) and Temp are 14610 x 146 x 220, they are different in class. rand(14610,146,220) is "double" and Temp is "single". May I know how do I solve this issue?

Example:

>> size(rand(14610,146,220))

ans =

14610 146 220

>> size(Temp)

ans =

14610 146 220

>> class(rand(14610,146,220))

ans =

'double'

>> class(Temp)

ans =

'single'

[Bruno Luong]

Try this

[~,i] = min(abs(A(:)-31.5814));
[i1 i2 i3] = ind2sub(size(A),i);
A(i1,i2,i3)

[Baiwen Ding]

Hi thanks for the answer it worked. Do you mind explaining the rationale behind the solution? Thanks.

[Bruno Luong]

Just look for the closest point to 31.5814, the metric is d=abs(x-31.5814). This solution doesn't need for fine tuning of the tolerance, so easier to work.