findnz
findnz(A)
Return a tuple (I, J, V) where I and J are the row and column indexes of the non-zero values in matrix A, and V is a vector of the non-zero values.
Examples
In the Julia programming language, the function findnz(A) returns a tuple (I, J, V) where I and J are the row and column indexes of the non-zero values in matrix A, and V is a vector of the non-zero values.
Example 1: Find non-zero elements in a matrix
julia> A = [1 0 0; 0 2 0; 0 0 3];
julia> I, J, V = findnz(A)
([1, 2, 3], [1, 2, 3], [1, 2, 3])In this example, the matrix A has non-zero elements at positions (1, 1), (2, 2), and (3, 3). The variables I, J, and V store the row indices, column indices, and non-zero values respectively.
Example 2: Find non-zero elements in a sparse matrix
julia> using SparseArrays
julia> A = sparse([1, 2, 3], [2, 1, 3], [4, 5, 6]);
julia> I, J, V = findnz(A)
([1, 2, 3], [2, 1, 3], [4, 5, 6])In this example, the sparse matrix A has non-zero elements at positions (1, 2), (2, 1), and (3, 3). The findnz function correctly returns the row indices, column indices, and non-zero values.
Mistake example: Trying to find non-zero elements in an empty matrix
julia> A = zeros(0, 0);
julia> I, J, V = findnz(A)
ERROR: DimensionMismatch("dimensions must match")In this example, an empty matrix A is used with findnz. However, since the dimensions of the matrix are empty, it results in a DimensionMismatch error. It is important to ensure that the matrix has non-zero elements before using findnz.
See Also
find, findfirst, findin, findlast, findmin, findn, findnext, findnz, findprev, rsearch, rsearchindex, searchsorted, searchsortedfirst, searchsortedlast, sort, sort!, sortcols, sortperm, sortperm!,User Contributed Notes
Add a Note
The format of note supported is markdown, use triple backtick to start and end a code block.