Method: Array#rotate

Defined in:
array.c

#rotate(count = 1) ⇒ Object

Returns a new array formed from self with elements rotated from one end to the other.

With non-negative numeric count, rotates elements from the beginning to the end:

[0, 1, 2, 3].rotate(2)   # => [2, 3, 0, 1]
[0, 1, 2, 3].rotate(2.1) # => [2, 3, 0, 1]

If count is large, uses count % array.size as the count:

[0, 1, 2, 3].rotate(22) # => [2, 3, 0, 1]

With a count of zero, rotates no elements:

[0, 1, 2, 3].rotate(0) # => [0, 1, 2, 3]

With negative numeric count, rotates in the opposite direction, from the end to the beginning:

[0, 1, 2, 3].rotate(-1) # => [3, 0, 1, 2]

If count is small (far from zero), uses count % array.size as the count:

[0, 1, 2, 3].rotate(-21) # => [3, 0, 1, 2]

Related: see Methods for Fetching.



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# File 'array.c', line 3289

static VALUE
rb_ary_rotate_m(int argc, VALUE *argv, VALUE ary)
{
    VALUE rotated;
    const VALUE *ptr;
    long len;
    long cnt = (rb_check_arity(argc, 0, 1) ? NUM2LONG(argv[0]) : 1);

    len = RARRAY_LEN(ary);
    rotated = rb_ary_new2(len);
    if (len > 0) {
        cnt = rotate_count(cnt, len);
        ptr = RARRAY_CONST_PTR(ary);
        len -= cnt;
        ary_memcpy(rotated, 0, len, ptr + cnt);
        ary_memcpy(rotated, len, cnt, ptr);
    }
    ARY_SET_LEN(rotated, RARRAY_LEN(ary));
    return rotated;
}