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Sort array of tuples and return the result.
f#

Hello,
I want to sort an array of tuples and return the sorted

array.

For example:

let aTuple = [|(1.0, 2.0);(1.0, 2.5);(2.0,3.5);(2.0,3.0)|]

The rule for sort is: to compare the first element of the

tuples, the one with the highest value is on the top; if the first element of

the tuples are the same for 2 or more tuples, then compare the second element

of the tuples, the lowest value is on the top.For example: for my example, the sorted result is like:

sortedTuple = [|(2.0,3.0) ; (2.0,3.5) ;(1.0, 2.0);(1.0, 2.5)|]

I need the sorted array.

Please show me the code.

Thanks and have a nice day!

.

When sorting tuples, you can use the fact that F# sorts tuples lexicographically. This means that the first element is ordered in ascending order and in case of a tie, it sorts at the second element in increasing order.

What you want to do is slightly different: you want to sort the first element descending (non-standard ordering) and the second ascending (standard ordering). Now here's a trick: sorting values x in descending order is the same as sorting -x in ascending order.

To perform this trick, you can use sortBy, which sorts using a transformed version of the data as keys:

1

let sortedTuple = aTuple |> Array.sortBy (fun (x,y) -> (-x,y))

Note that this doesn't transform the data itself, it just sorts on the transformed version of the input data.

By on 1/10/2010 6:09 AM ()

Hello, Cfern:
Thank you very much, your code works.
Also, thank you again for the good explanation.
Have a nice day!

By on 1/10/2010 7:23 AM ()

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