How to convert a matrix into a sparse matrix [duplicate]

If I have a matrix:

row 1)1 0 0 4
row 2)0 0 0 0
row 3)5 1 0 0
row 4)0 5 0 0
row 5)0 0 0 9


How would I put it in a sparse matrix format:

a(0)(0) = ? a(0)(1) = ? a(0)(2) = ?
a(1)(0) = ? a(1)(1) = ? a(1)(2) = ?
a(2)(0) = ? a(2)(1) = ? a(2)(2) = ?
a(3)(0) = ? a(3)(1) = ? a(3)(2) = ?
a(4)(0) = ? a(4)(1) = ? a(4)(2) = ?
a(5)(0) = ? a(5)(1) = ? a(5)(2) = ?


I've tried looking on the internet but I couldn't find any help telling me how to do it.

• (I believe this is a dupe, but I can't find the other thread.) Apply SparseArray[] to your original matrix to get the sparse form, e.g. SparseArray[IdentityMatrix[4]]. Mar 5, 2016 at 1:18
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With

a = {{1, 0, 0, 4},
{0, 0, 0, 0},
{5, 1, 0, 0},
{0, 5, 0, 0},
{0, 0, 0, 9}};


Then

sa = SparseArray[a]


Since SparseArray takes the default to be 0.

Hope this helps.

According to the link (How to | Work with Sparse Matrices) : "https://reference.wolfram.com/language/howto/WorkWithSparseMatrices.html". Hope this help.

mat = SparseArray[{{1, 0, 0, 4}, {0, 0, 0, 0}, {5, 1, 0, 0}, {0, 5, 0,0}, {0, 0, 0, 9}}]

mat // MatrixForm

a = SparseArray[{{1,1} -> 1, {3,1} -> 5, ....}]