[Numpy-discussion] Sorting large numbers of co-ordinate pairs

[Dinesh B Vadhia]

I have a large number (> 1bn) of (32-bit) integer co-ordinates (i, j) in a file.  The i are ordered and the j unordered eg.
...
6940, 22886
6940, 38277
6940, 43788
7007, 0
7007, 2362
7007, 34
etc.
...

I want to create (j, i) with j ordered and i unordered and store in a file ie.
...
38277, 567
38277, 90023
38277, 6940
43788, 5672
43788, 98
etc
...

My computers have sufficient memory (2gb on one and 8gb on another).

Any ideas how I could do this using numpy?

Dinesh
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