find

Arguments

x

Vector, matrix, or hypermatrix of booleans or of numbers. All non-zero numbers are considered as %T. Sparse matrices are accepted.

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

row vector of linearized indices of %T or non-zero elements, or empty matrix []

i1, i2, ..

row vectors of directional indices, or empty matrix []

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

With input booleans:

A = [%F %T %T %F ; %T %F %F %T]
find(A)
find(A,2)

--> A = [%F %T %T %F ; %T %F %F %T]
 A  =
  F T T F
  T F F T

--> find(A)
 ans  =
   2.   3.   5.   8.

--> find(A,2)
 ans  =
   2.   3.

With input numbers:

B = [0 -1 0 3 ; 0 -1 -0.4 0]
find(B)
[i, j] = find(B);
[i' j']

--> B = [0 -1 0 3 ; 0 -1 -0.4 0]
 B  =
   0.  -1.   0.    3.
   0.  -1.  -0.4   0.

--> find(B)
 ans  =
   3.   4.   6.   7.

--> [i, j] = find(B);
--> [i' j']
 ans  =
   1.   2.
   2.   2.
   2.   3.
   1.   4.

With an input hypermatrix of numbers:

E = grand(2,5,2,"uin",1,6)
find(E < 4)

--> E = grand(2,5,2,"uin",1,6)
 E  =
(:,:,1)
   1.   6.   5.   5.   4.
   6.   5.   3.   4.   4.
(:,:,2)
   2.   4.   3.   6.   5.
   5.   6.   6.   6.   4.

--> find(E < 4)
 ans  =
   1.   6.   11.   15.

With an input numerical or boolean sparse matrix:

C = [0  3  7  0  9  0
     0  4  0  0  5  0
     6  0  1  0  3  8
    ];
C = sparse(C);
find(C)
find(C, 4)

// With input boolean sparse
D = C > 4
full(D)
find(D)

--> C = sparse(C);
--> find(C)
 ans  =
    3.    4.    5.    7.    9.    13.    14.    15.    18.

-->find(C, 4)
 ans  =
    3.    4.    5.    7.

--> // With input boolean sparse
--> D = C > 4
 D  =
(  3,  6) sparse boolean matrix
(  1,  3)   T
(  1,  5)   T
(  2,  5)   T
(  3,  1)   T
(  3,  6)   T

--> full(D)
 ans  =
  F F T F T F
  F F F F T F
  T F F F F T

-->find(D)
 ans  =
    3.    7.    13.    14.    18.

With the result of a boolean element-wise condition on texts:

beers = ["Desperados", "Leffe", "Kronenbourg", "Heineken"];
find(beers == "Leffe")
find(beers == "1664")

--> find(beers == "Leffe")
 ans  =
   2.

--> find(beers == "1664")
 ans  =
    []

Addressing selected elements:

// a) Through their linearized indices:
H = [ 0  -2  -8  4  -5  -1
     -2   2  -9  5   0   1
    ];
L = H;
L(find(L < 0)) = -10

// b) Directly through the array of their boolean status:
L = H;
L(L < 0) = -10

--> // a) Through their linearized indices:
--> H = [ 0  -2  -8  4  -5  -1
  >      -2   2  -9  5   0   1
  >     ];
--> L = H;
--> L(find(L < 0)) = -10
 L  =
   0.   -10.  -10.   4.  -10.  -10.
  -10.   2.   -10.   5.   0.    1.

--> // b) Directly through the array of their boolean status:
--> L = H;
--> L(L < 0) = -10
 L  =
   0.   -10.  -10.   4.  -10.  -10.
  -10.   2.   -10.   5.   0.    1.

See also

• vectorfind — locates occurences of a (wildcarded) vector in a matrix or hypermatrix
• grep — find matches of a string in a vector of strings
• findobj — find an object with specified property
• boolean — Scilab Objects, boolean variables and operators & | ~