How to reshape matrices in Mathematica

When manipulating matrices it is often convenient to change their shape. For instance, to turn an N x M sized matrix into a vector of length N X M. In MATLAB a reshape function exists:

RESHAPE(X,M,N) returns the M-by-N matrix whose elements are taken columnwise from X. An error results if X does not have M*N elements.

In the case of converting between a matrix and vector I can use the Mathematica function Flatten which takes advantage of Mathematica's nested list representation for matrices. As a quick example, suppose I have a matrix X:

With Flatten[X] I can get the vector {1,2,3,...,16}. But what would be far more useful is something akin to applying Matlab's reshape(X,2,8) which would result in the following Matrix:

This would allow creation of arbitrary matrices as long as the dimensions equal N*M. As far as I can tell, there isn't anything built in which makes me wonder if someone hasn't coded up a Reshape function of their own.

``````Reshape[mtx_, _, n_] := Partition[Flatten[mtx], n]
``````

I know this is an old thread but for the sake of the archives and google searches I've got a more general way that allows a length m*n*... list to be turned into an m*n*... array:

``````Reshape[list_, shape__] := Module[{i = 1},
NestWhile[Partition[#, shape[[i]]] &, list, ++i <= Length[shape] &]
]
``````

Eg:

``````In:= Reshape[Range[8], {2, 2, 2}]

Out:= {{{1, 2}, {3, 4}}, {{5, 6}, {7, 8}}}
``````
``````Reshape[list_, dimensions_] :=
First[Fold[Partition[#1, #2] &, Flatten[list], Reverse[dimensions]]]
``````

Example Usage:

``````In: Reshape[{1,2,3,4,5,6},{2,3}]

Out: {{1,2,3},{4,5,6}}
``````

This works with arrays of arbitrary depth.

ArrayReshape does exactly that.

``````{{1, 2, 3}, {4, 5, 6}} // MatrixForm