ArrayReshape

ArrayReshape[list, dims] arranges the elements of list into a rectangular array with dimensions dims.

ArrayReshape[list, dims, padding] uses the specified padding if list does not contain enough elements.

Examples

Reshape a flat list into a matrix:

ArrayReshape[Range[6], {2, 3}]
(* {{1, 2, 3}, {4, 5, 6}} *)

Reshape with padding:

ArrayReshape[{1, 2, 3}, {2, 3}, 0]
(* {{1, 2, 3}, {0, 0, 0}} *)

Please visit the official Wolfram Language Reference for more details.