5.10) Finding elements in arrays

find is a very useful function for finding the indices (and hence the values) of array elements you are interested in.

In its most basic form, it finds the indices of non-zero elements in an array
In combination with a logical condition, it finds the indices of elements that satisfy the condition.
Syntax:

[matlab]
>> [z]=find(X); % z is the linear indices where X is non-zero.
[/matlab]
[matlab]
>> [x y]=find(X); % If X is a matrix, "find" can return
>> % the row and column subscripts of all cells that are non-zero.
[/matlab]
[matlab]
>> [x y v]=find(X); % If X is a matrix, "x" and "y" will get
>> % the row and column subscripts of all cells that are non-zero,
>> % and "v" will get the actual values.
[/matlab]

In all cases, "X" can also be a logical function of X:

[matlab]
>> A=magic(4);
>> [x y]=find(A>12)
x= 1 y= 1
4 2
4 3
1 4
>> z=find(A>12);
>> % Linear indices
>> A(z)=
16 14 15 13
>> % These are the indices
>> % where A > 12.
[/matlab]

[matlab]
>> A=magic(5);
>> B=eye(5);
>> z=find((B==1)&(A>10))
>> A(z)=
17 13 21
>> % These are indices where
>> % A>10 and B==1
[/matlab]

First Page

Last Page