find - find indices of boolean vector or matrix true elements

Calling Sequence

[ii]=find(x [,nmax])

[i1,i2,..]=find(x [,nmax])

Parameters

• x : may be a boolean vector, a boolean matrix, a boolean hypermatrix, a "standard" matrix or hypermatrix
• nmax : an integer giving the maximum number of indices to return. The default value is -1 which stands for "all". This option can be used for efficiency, to avoid searching all indices.
• ii, i1, i2, .. : integer vectors of indices or empty matrices

Description

If x is a boolean matrix,

ii=find(x) returns the vector of indices i for which x(i) is "true". If no true element found find returns an empty matrix.

[i1,i2,..]=find(x) returns vectors of indices i1 (for rows) and i2 (for columns),.. such that x(i1(n),i2(n),..) is "true". If no true element found find returns empty matrices in i1, i2, ...

if x is a standard matrix or hypermatrix find(x) is interpreted as find(x<>0)

find([]) returns []

Examples

A=rand(1,20);
w=find(A<0.4)
A(w)
w=find(A>100) 

B=rand(1,20);
w=find(B<0.4,2) //at most 2 returned values

H=rand(4,3,5); //an hypermatrix
[i,j,k]=find(H>0.9)  

H(i(1),j(1),k(1))
 

See Also

boolean  extraction  insertion