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Don't create dict for empty lists #5348

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Jul 22, 2018
Merged

Don't create dict for empty lists #5348

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4d67261
Shortcut empty arrays for groupBy
forki Jul 18, 2018
28e2de1
Shortcut empty seqs for groupBy
forki Jul 18, 2018
352c139
Don't create dict for empty lists
forki Jul 18, 2018
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4 changes: 3 additions & 1 deletion src/fsharp/FSharp.Core/array.fs
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Expand Up @@ -405,10 +405,12 @@ namespace Microsoft.FSharp.Collections
loop 0

let inline groupByImpl (comparer:IEqualityComparer<'SafeKey>) (keyf:'T->'SafeKey) (getKey:'SafeKey->'Key) (array: 'T[]) =
let length = array.Length
if length = 0 then Microsoft.FSharp.Primitives.Basics.Array.zeroCreateUnchecked 0 else
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Maybe it's time to add empty arrays singleton? #5066 (comment)

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yes. I could use them in many places

let dict = Dictionary<_,ResizeArray<_>> comparer

// Build the groupings
for i = 0 to (array.Length - 1) do
for i = 0 to length - 1 do
let v = array.[i]
let safeKey = keyf v
let mutable prev = Unchecked.defaultof<_>
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4 changes: 4 additions & 0 deletions src/fsharp/FSharp.Core/local.fs
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Expand Up @@ -196,6 +196,10 @@ module internal List =
cons

let groupBy (comparer:IEqualityComparer<'SafeKey>) (keyf:'T->'SafeKey) (getKey:'SafeKey->'Key) (list: 'T list) =
match list with
| [] -> []
| _ ->

let dict = Dictionary<_, _ list []> comparer

// Build the groupings
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2 changes: 2 additions & 0 deletions src/fsharp/FSharp.Core/seq.fs
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Expand Up @@ -1032,6 +1032,8 @@ namespace Microsoft.FSharp.Collections
let inline groupByImpl (comparer:IEqualityComparer<'SafeKey>) (keyf:'T->'SafeKey) (getKey:'SafeKey->'Key) (seq:seq<'T>) =
checkNonNull "seq" seq

if isEmpty seq then empty else

let dict = Dictionary<_,ResizeArray<_>> comparer

// Previously this was 1, but I think this is rather stingy, considering that we are already paying
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