F# dictionary entry grouping and sort issue

Saturday, March 02, 2013 6:54 PM

0

Hello,

let dNum = new Dictionary<int, decimal>()

dNum.Add(0, 0M)

dNum.Add(1, 10M)

dNum.Add(2, 20M)

dNum.Add(3, 30M)

dNum.Add(4, 40M)

dNum.Add(5, 30M)

dNum.Add(6, 20M)

I want to do this:

Let’s divide the dictionary entries into groups of 3 consecutive entries, and check to see if the 3 entries are in ascending order or descending order, and if in ascending order, and if the first entry is less than the last entry by 10+, then create a new dictionary and add the entry as +1; and if in descending order, and if the first entry is more than the last entry by 10+, then create a new dictionary and add the entry as -1, otherwise, create a new dictionary and add the entry as 0.

For example: in the above example: dNum entries: (1, 10M); (2, 20M); (3, 30M), then new dictionary:

dNumSort.Add(1, 1)

The final result for my example will be like this:

let dNumSort = new Dictionary<int, int>()

dNumSort.Add(0, 1)

dNumSort.Add(1, 1)

dNumSort.Add(2, 1)

dNumSort.Add(3, 0)

dNumSort.Add(4, -1)

I think I can do this using non-functional way, but can’t figure out the functional way.

To divide the dictionary entries into groups of 3 consecutive entries, I can use the following:

let group3 = dNum

|> Seq.map (fun (KeyValue(k,v)) -> v)

|> Seq.windowed 3

However, how to check to see if the group is in ascending or descending order and others seem not easy to put together.

Any idea is welcome!
- Reply
- Quote

All Replies

Sunday, March 03, 2013 12:23 AM

It's a little ugly (not really overthought the thing) but seems correct

open System.Collections.Generic

let dNum = Dictionary (dict [ 0, 0M; 1, 10M; 2, 20M; 3, 30M; 4, 40M; 5, 30M; 6, 20M ])

let result =
  Dictionary (
    dNum
    |> Seq.map (|KeyValue|)
    |> Seq.windowed 3
    |> Seq.map (fun arr ->
      let (k, v1), (_, v2), (_, v3) = arr.[0], arr.[1], arr.[2]
    // alternative for previous line but give a warning for incomplete match
    // but we know for sure the array has only 3 items
    //|> Seq.map (fun [| k, v1; _, v2; _, v3 |] ->
      k,
      if abs (v1 - v3) >= 10M then
        if v1 <= v2 && v2 <= v3 then 1
        elif v1 >= v2 && v2 >= v3 then -1
        else 0
      else 0)
    |> dict)

Forgive my writing, English isn't my native language.

Marked As Answer by zydjohn Saturday, March 09, 2013 8:46 AM

Saturday, March 09, 2013 8:47 AM

0

Thank you very much!

Your code works!

Thanks and have a nice weekend.

John
- Reply
- Quote