find (MATLAB Functions)

Find indices and values of nonzero elements

Syntax

k = find(x)
[i,j] = find(X)
[i,j,v] = find(X)

Description

k = find(X) returns the indices of the array X that point to nonzero elements. If none is found, find returns an empty matrix.

[i,j] = find(X) returns the row and column indices of the nonzero entries in the matrix X. This is often used with sparse matrices.

[i,j,v] = find(X) returns a column vector v of the nonzero entries in X, as well as row and column indices.

In general, find(X) regards X as X(:), which is the long column vector formed by concatenating the columns of X.

Examples

[i,j,v] = find(X~=0) produces a vector v with all 1s, and returns the row and column indices.

Some operations on a vector

x = [11  0  33  0  55]';
find(x)

ans =

     1
     3
     5

find(x == 0)

ans =

     2
     4

find(0 < x & x < 10*pi)

ans =

     1

And on a matrix

M = magic(3)

M =

     8     1     6
     3     5     7
     4     9     2

[i,j,v] = find(M > 6)

i =            j =          v =

     1              1            1
     3              2            1
     2              3            1

filter2 findall