reshape#

Purpose#

Reshapes a dataframe, matrix or string array.

Format#

y = reshape(x, r[, c])#
Parameters:

  • x (NxK matrix) – data

  • r (scalar) – new row dimension. If -1 is passed in, the row dimension will be inferred based on the size of the input data and the column dimension.

  • c (scalar) – Optional input, new column dimension. If c is not passed in a default value of 1 will be used. If -1 is passed in, the column dimension will be inferred based on the size of the input data and the row dimension.

Returns:

y (RxC matrix) – created from the elements of x.

Examples#

Repeating a scalar element#

// Create a 3x1 vector of 5's
x = reshape(5, 3);

After the above code, x will equal:

5
5
5

// Create a 1x4 row vector of 5's
x = reshape(5, 1, 4);

After the above code, x will equal:

5   5   5   5

Examples with a -1 row or column input#

// Create a 3x4 matrix
x = { 1  2  3  4,
      5  6  7  8,
      9 10 11 12 };

y = reshape(x, 2, -1);

After the above code, y will equal:

1   2   3    4    5    6
7   8   9   10   11   12

Continuing with the x from above:

y = reshape(x, -1, 3);

 1    2    3
 4    5    6
 7    8    9
10   11   12

Other basic examples#

y = reshape(x, 2, 6);

        1  2  3  4
if x =  5  6  7  8  then y = 1  2  3  4  5  6
        9 10 11 12           7  8  9 10 11 12

        1  2  3
if x =  4  5  6  then y = 1  2  3  4  5  6
        7  8  9           7  8  9  1  2  3

        1  2  3  4  5
if x =  6  7  8  9 10  then y = 1  2  3  4  5  6
       11 12 13 14 15           7  8  9 10 11 12

if x = 1  2  then y = 1 2 3 4 1 2
       3  4           3 4 1 2 3 4

if x = 1  then y = 1 1 1 1 1 1
                   1 1 1 1 1 1

Remarks#

Matrices (as well as dataframes and string arrays) are stored in row major order.

The first c elements are put into the first row of y, the second in the second row, and so on. If there are more elements in x than in y, the remaining elements are discarded. If there are not enough elements in x to fill y, then when reshape runs out of elements, it goes back to the first element of x and starts getting additional elements from there.

See also

Functions submat(), vec()

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