Indexing

There are several ways of referencing values. ArrayFire uses parenthesis for subscripted referencing instead of the traditional square bracket notation. Indexing is zero-based, i.e. the first element is at index zero (A(0)). Indexing can be done with mixtures of:

• integer scalars
• seq() representing a linear sequence
• end representing the last element of a dimension
• span representing the entire dimension
• row(i) or col(i) specifying a single row/column
• rows(first,last) or cols(first,last) specifying a span of rows or columns

See Indexing for the full listing.

    array A = array(seq(1,9), 3, 3);
    af_print(A);

    af_print(A(0));    // first element
    af_print(A(0,1));  // first row, second column

    af_print(A(end));   // last element
    af_print(A(-1));    // also last element
    af_print(A(end-1)); // second-to-last element

    af_print(A(1,span));       // second row
    af_print(A.row(end));      // last row
    af_print(A.cols(1,end));   // all but first column

    float b_host[] = {0,1,2,3,4,5,6,7,8,9};
    array b(10, 1, b_host);
    af_print(b(seq(3)));
    af_print(b(seq(1,7)));
    af_print(b(seq(1,7,2)));
    af_print(b(seq(0,end,2)));

You can set values in an array:

    array A = constant(0, 3, 3);
    af_print(A);

    // setting entries to a constant
    A(span) = 4;        // fill entire array
    af_print(A);

    A.row(0) = -1;      // first row
    af_print(A);

    A(seq(3)) = 3.1415; // first three elements
    af_print(A);

    // copy in another matrix
    array B = constant(1, 4, 4, s32);
    B.row(0) = randu(1, 4, f32); // set a row to random values (also upcast)

Use one array to reference into another.

    float h_inds[] = {0, 4, 2, 1}; // zero-based indexing
    array inds(1, 4, h_inds);
    af_print(inds);

    array B = randu(1, 4);
    af_print(B);

    array c = B(inds);        // get
    af_print(c);

    B(inds) = -1;             // set to scalar
    B(inds) = constant(0, 4); // zero indices
    af_print(B);