find (MATLAB Function Reference)

find	Examples See Also

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