Getting equivalent elements in a range/array

[Andrej M.]

I want to turn this:
auto arr = [1, 1, 2, 3, 4, 4];

into this:
auto arr2 = [[1, 1], [2], [3], [4, 4]];

I want an array of arrays of the same elements. Lazy or not, I don't care.

I thought I could get away with this inside some while loop:
auto equals = array(filter!"a == b"(arr));
arr = arr[equals.length-1..$];

Nope.

I need this for some buffered output, where the requirement is the elements of 
the buffer all need to have the same properties so a function can output a 
buffer of elements in one call instead of calling the function for each element 
(the function call is expensive).