subvec#

Purpose#

Extracts an Nx1 vector of elements from an NxK matrix.

Format#

y = subvec(x, ci)#
Parameters:

  • x (NxK matrix) – data

  • ci (Nx1 vector) – column indices

Returns:

y (Nx1 vector) – contains the elements in x indicated by ci.

Examples#

// Create an additive sequence from 1-12, i.e. 1, 2, 3,...12
x = seqa(1, 1, 12);

// Reshape the sequential vector 'x' into a 4x3 matrix
x = reshape(x, 4, 3);

// The column indices (one per row of 'x') indicating which
// values to extract from 'x'
ci = { 2, 3, 1, 3 };

// Extract subvector from 'x' and assign it to 'y'
y = subvec(x, ci);

After the above code, x and y are equal to:

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

     2
 y = 6
     7
    12

Remarks#

Each element of y is from the corresponding row of x and the column set by the corresponding row of ci. In other words, \(y[i] = x[i, ci[i]]\).

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