Method: Numo::NArray#diagonal

Defined in:
ext/numo/narray/data.c

#diagonal([offset,axes]) ⇒ Numo::NArray

Returns a diagonal view of NArray

Examples:

a = Numo::DFloat.new(4,5).seq
# => Numo::DFloat#shape=[4,5]
# [[0, 1, 2, 3, 4],
#  [5, 6, 7, 8, 9],
#  [10, 11, 12, 13, 14],
#  [15, 16, 17, 18, 19]]
b = a.diagonal(1)
# => Numo::DFloat(view)#shape=[4]
# [1, 7, 13, 19]

b.store(0)
a
# => Numo::DFloat#shape=[4,5]
# [[0, 0, 2, 3, 4],
#  [5, 6, 0, 8, 9],
#  [10, 11, 12, 0, 14],
#  [15, 16, 17, 18, 0]]

b.store([1,2,3,4])
a
# => Numo::DFloat#shape=[4,5]
# [[0, 1, 2, 3, 4],
#  [5, 6, 2, 8, 9],
#  [10, 11, 12, 3, 14],
#  [15, 16, 17, 18, 4]]

Parameters:

  • offset (Integer) —

    Diagonal offset from the main diagonal. The default is 0. k>0 for diagonals above the main diagonal, and k<0 for diagonals below the main diagonal.

  • axes (Array) —

    Array of axes to be used as the 2-d sub-arrays from which the diagonals should be taken. Defaults to last-two axes ([-2,-1]).

Returns:



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# File 'ext/numo/narray/data.c', line 616

static VALUE
na_diagonal(int argc, VALUE *argv, VALUE self)
{
    int  i, k, nd;
    size_t  j;
    size_t *idx0, *idx1, *diag_idx;
    size_t *shape;
    size_t  diag_size;
    ssize_t stride, stride0, stride1;
    narray_t *na;
    narray_view_t *na1, *na2;
    VALUE view;
    VALUE vofs=0, vaxes=0;
    ssize_t kofs;
    size_t k0, k1;
    int ax[2];

    // check arguments
    if (argc>2) {
        rb_raise(rb_eArgError,"too many arguments (%d for 0..2)",argc);
    }

    for (i=0; i<argc; i++) {
        switch(TYPE(argv[i])) {
        case T_FIXNUM:
            if (vofs) {
                rb_raise(rb_eArgError,"offset is given twice");
            }
            vofs = argv[i];
            break;
        case T_ARRAY:
            if (vaxes) {
                rb_raise(rb_eArgError,"axes-array is given twice");
            }
            vaxes = argv[i];
            break;
        }
    }

    if (vofs) {
        kofs = NUM2SSIZET(vofs);
    } else {
        kofs = 0;
    }

    GetNArray(self,na);
    nd = na->ndim;
    if (nd < 2) {
        rb_raise(nary_eDimensionError,"less than 2-d array");
    }

    if (vaxes) {
        if (RARRAY_LEN(vaxes) != 2) {
            rb_raise(rb_eArgError,"axes must be 2-element array");
        }
        ax[0] = NUM2INT(RARRAY_AREF(vaxes,0));
        ax[1] = NUM2INT(RARRAY_AREF(vaxes,1));
        if (ax[0]<-nd || ax[0]>=nd || ax[1]<-nd || ax[1]>=nd) {
            rb_raise(rb_eArgError,"axis out of range:[%d,%d]",ax[0],ax[1]);
        }
        if (ax[0]<0) {ax[0] += nd;}
        if (ax[1]<0) {ax[1] += nd;}
        if (ax[0]==ax[1]) {
            rb_raise(rb_eArgError,"same axes:[%d,%d]",ax[0],ax[1]);
        }
    } else {
        ax[0] = nd-2;
        ax[1] = nd-1;
    }

    // Diagonal offset from the main diagonal.
    if (kofs >= 0) {
        k0 = 0;
        k1 = kofs;
        if (k1 >= na->shape[ax[1]]) {
            rb_raise(rb_eArgError,"invalid diagonal offset(%"SZF"d) for "
                     "last dimension size(%"SZF"d)",kofs,na->shape[ax[1]]);
        }
    } else {
        k0 = -kofs;
        k1 = 0;
        if (k0 >= na->shape[ax[0]]) {
            rb_raise(rb_eArgError,"invalid diagonal offset(=%"SZF"d) for "
                     "last-1 dimension size(%"SZF"d)",kofs,na->shape[ax[0]]);
        }
    }

    diag_size = MIN(na->shape[ax[0]]-k0,na->shape[ax[1]]-k1);

    // new shape
    shape = ALLOCA_N(size_t,nd-1);
    for (i=k=0; i<nd; i++) {
        if (i != ax[0] && i != ax[1]) {
            shape[k++] = na->shape[i];
        }
    }
    shape[k] = diag_size;

    // new object
    view = na_s_allocate_view(rb_obj_class(self));
    na_copy_flags(self, view);
    GetNArrayView(view, na2);

    // new stride
    na_setup_shape((narray_t*)na2, nd-1, shape);
    na2->stridx = ALLOC_N(stridx_t, nd-1);

    switch(na->type) {
    case NARRAY_DATA_T:
    case NARRAY_FILEMAP_T:
        na2->offset = 0;
        na2->data = self;
        stride = stride0 = stride1 = nary_element_stride(self);
        for (i=nd,k=nd-2; i--; ) {
            if (i==ax[1]) {
                stride1 = stride;
                if (kofs > 0) {
                    na2->offset = kofs*stride;
                }
            } else if (i==ax[0]) {
                stride0 = stride;
                if (kofs < 0) {
                    na2->offset = (-kofs)*stride;
                }
            } else {
                SDX_SET_STRIDE(na2->stridx[--k],stride);
            }
            stride *= na->shape[i];
        }
        SDX_SET_STRIDE(na2->stridx[nd-2],stride0+stride1);
        break;

    case NARRAY_VIEW_T:
        GetNArrayView(self, na1);
        na2->data = na1->data;
        na2->offset = na1->offset;
        for (i=k=0; i<nd; i++) {
            if (i != ax[0] && i != ax[1]) {
                if (SDX_IS_INDEX(na1->stridx[i])) {
                    idx0 = SDX_GET_INDEX(na1->stridx[i]);
                    idx1 = ALLOC_N(size_t, na->shape[i]);
                    for (j=0; j<na->shape[i]; j++) {
                        idx1[j] = idx0[j];
                    }
                    SDX_SET_INDEX(na2->stridx[k],idx1);
                } else {
                    na2->stridx[k] = na1->stridx[i];
                }
                k++;
            }
        }
        if (SDX_IS_INDEX(na1->stridx[ax[0]])) {
            idx0 = SDX_GET_INDEX(na1->stridx[ax[0]]);
            diag_idx = ALLOC_N(size_t, diag_size);
            if (SDX_IS_INDEX(na1->stridx[ax[1]])) {
                idx1 = SDX_GET_INDEX(na1->stridx[ax[1]]);
                for (j=0; j<diag_size; j++) {
                    diag_idx[j] = idx0[j+k0] + idx1[j+k1];
                }
            } else {
                stride1 = SDX_GET_STRIDE(na1->stridx[ax[1]]);
                for (j=0; j<diag_size; j++) {
                    diag_idx[j] = idx0[j+k0] + stride1*(j+k1);
                }
            }
            SDX_SET_INDEX(na2->stridx[nd-2],diag_idx);
        } else {
            stride0 = SDX_GET_STRIDE(na1->stridx[ax[0]]);
            if (SDX_IS_INDEX(na1->stridx[ax[1]])) {
                idx1 = SDX_GET_INDEX(na1->stridx[ax[1]]);
                diag_idx = ALLOC_N(size_t, diag_size);
                for (j=0; j<diag_size; j++) {
                    diag_idx[j] = stride0*(j+k0) + idx1[j+k1];
                }
                SDX_SET_INDEX(na2->stridx[nd-2],diag_idx);
            } else {
                stride1 = SDX_GET_STRIDE(na1->stridx[ax[1]]);
                na2->offset += stride0*k0 + stride1*k1;
                SDX_SET_STRIDE(na2->stridx[nd-2],stride0+stride1);
            }
        }
        break;
    }
    return view;
}