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CsrMatrix.ToDense

The same matrix with its zeros written out, for inspection.

public double[,] ToDense()

Returns — double[,] of RowCount × ColumnCount, every cell present, the stored values in their places and zeros everywhere else.

Example — the cell that says the appears twice in the third document.

using Lodestar.Text.Vectorization;

string[] docs = ["the cat eats", "the dog eats", "the cat and the dog"];
var cv = new CountVectorizer();
CsrMatrix counts = cv.FitTransform(docs);

// Features are sorted: and, cat, dog, eats, the — so "the" is column 4.
double[,] dense = counts.ToDense();
double theInThird = dense[2, 4];  // => 2

Remarks — allocates RowCount × ColumnCount doubles, which is exactly the array the sparse layout exists to avoid. On the three-document corpus above that is fifteen cells; on a real corpus it is the number that made sparsity necessary in the first place. Reach for it to look at a small matrix, to hand a small one to something that wants a rectangular array, or in a test — not as a step in a pipeline.

To read one cell without materialising the rest, walk RowPointers and ColumnIndices directly; to reduce the whole matrix against a vector, Multiply does it without densifying.

Applies to — net10.0, netstandard2.0.

See also — CsrMatrix, CsrMatrix.Multiply.