Partitioning an array of n-tuples

[graphicsRat]

I'd like to partition an array of n-tuples based on whether the one of the elements of a tuple is a specified number m.

For example the sequence of 2-tuples:

1 , 4 ,
1 , 3 ,
2 , 3 ,
1 , 2 ,
2 , 2 ,
3 , 2 ,
1 , 1 ,
2 , 1 ,
3 , 1 ,
4 , 1


Will be partitioned as follows, if m = 4:

1 , 4 ,
4 , 1 ,_________
1 , 3 ,
2 , 3 ,
1 , 2 ,
2 , 2 ,
3 , 2 ,
1 , 1 ,
2 , 1 ,
3 , 1


Unfortunately the examples given in the docs are based on partitioning arrays of scalars. FYI, my data is not laid out as a structure of arrays because I think doing so will kill coalescence of read requests because each element of a tuple will be equally spaced throughout the array. The partition can either be in-place or a copy of the input -- whichever is easier to implement.