gofn

module
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 Go to latest Published: May 1, 2026 License: GPL-3.0

README

gofn

Coverage Go

library to use golang functional

Summary

Usage

array.Filter

Filter a array , with a function that return a boolean.


data := []int{1, 2, 3, 4, 5, 6, 7, 8, 9, 10}

    // filter
    result := array.Filter(data, func(i int) bool {
        return i%2 == 0
    })

    fmt.Println(result) // [2 4 6 8 10]
array.Find

Find a element in the array , with a function that return a boolean.


data := []int{1, 2, 3, 4, 5, 6, 7, 8, 9, 10}

    // filter
    result := array.Find(data, func(i int) bool {
        return i%2 == 0
    })

    fmt.Println(result) // 2
array.Map

Map a array , with a function that return a value.


data := []int{1, 2, 3, 4, 5, 6, 7, 8, 9, 10}

    // filter
    result := array.Map(data, func(i int) int {
        return i * 2
    })

    fmt.Println(result) // [2 4 6 8 10 12 14 16 18 20]
array.FlatMap

FlatMap a array , with a function that return a slice.


a := []int{1, 2, 3, 4, 5}
b := array.FlatMap(a, func(x int) []int { return []int{x, x * 2} })

fmt.Println(b) // [1 2 2 4 3 6 4 8 5 10]
array.Reduce

Reduce a array , with a function that return a value.


data := []int{1, 2, 3, 4, 5, 6, 7, 8, 9, 10}

    // filter
    result := array.Reduce(data, func(i, j int) int {
        return i + j
    })

    fmt.Println(result) // 55
array.Any

Check if any element in the array match the condition.


data := []int{1, 2, 3, 4, 5, 6, 7, 8, 9, 10}

    // filter
    result := array.Any(data, func(i int) bool {
        return i%2 == 0
    })

    fmt.Println(result) // true
array.Some

Check if some element in the array match the condition.


data := []int{1, 2, 3, 4, 5, 6, 7, 8, 9, 10}

    // filter
    result := array.Some(data, func(i int) bool {
        return i%2 == 0
    })

    fmt.Println(result) // true
array.Every

Check if every element in the array match the condition.


data := []int{1, 2, 3, 4, 5, 6, 7, 8, 9, 10}

    // filter
    result := array.Every(data, func(i int) bool {
        return i%2 == 0
    })

    fmt.Println(result) // false
array.Sum

Sum all elements in the array.


data := []int{1, 2, 3, 4, 5, 6, 7, 8, 9, 10}

    // filter
    result := array.Sum(data)

    fmt.Println(result) // 55
array.Max

Get the max element in the array.


data := []int{1, 2, 3, 4, 5, 6, 7, 8, 9, 10}

    // filter
    result := array.Max(data)

    fmt.Println(result) // 10
array.Min

Get the min element in the array.


data := []int{1, 2, 3, 4, 5, 6, 7, 8, 9, 10}

    // filter
    result := array.Min(data)

    fmt.Println(result) // 1
array.Product

Get the product of all elements in the array.


data := []int{1, 2, 3, 4, 5, 6, 7, 8, 9, 10}

    // filter
    result := array.Product(data)

    fmt.Println(result) // 3628800
array.Reverse

Reverse te order of the array.


data := []int{1, 2, 3, 4, 5, 6, 7, 8, 9, 10}

    // filter
    result := array.Reverse(data)

    fmt.Println(result) // [10 9 8 7 6 5 4 3 2 1]
array.Shuffle

Shuffle the array.


data := []int{1, 2, 3, 4, 5, 6, 7, 8, 9, 10}

    // filter
    result := array.Shuffle(data)

    fmt.Println(result) // [10 9 8 7 6 5 4 3 2 1]
array.Unique

Get unique elements in the array.


data := []int{1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10}

    // filter
    result := array.Unique(data)

    fmt.Println(result) // [1 2 3 4 5 6 7 8 9 10]
array.Union

Get union of two arrays.


a := []int{1, 2, 3, 4, 5}
b := []int{6, 7, 8, 9, 10}

    // filter
    result := array.Union(a, b)

    fmt.Println(result) // [1 2 3 4 5 6 7 8 9 10]
array.Fill

Fill the array with a value.


a := []int{1, 2, 3, 4, 5}
b := array.Fill(a, 0, len(a), 0)

fmt.Println(b) // [0 0 0 0 0]
array.Join

Join the array with a separator.


a := []int{1, 2, 3, 4, 5}
b := array.Join(a, "-")

fmt.Println(b) // 1-2-3-4-5
array.Pop

Pop the last element of the array, and return the removed element and the new array.


a := []int{1, 2, 3, 4, 5}
b, c := array.Pop(a)

fmt.Println(b) // 5
fmt.Println(c) // [1 2 3 4]
array.Push

Push an element to the array, and return the new array.


a := []int{1, 2, 3, 4, 5}
b := array.Push(a, 6)

fmt.Println(b) // [1 2 3 4 5 6]
array.Shift

Shift the first element of the array, and return the removed element and the new array.


a := []int{1, 2, 3, 4, 5}
b, c := array.Shift(a)

fmt.Println(b) // 1
fmt.Println(c) // [2 3 4 5]
array.Sort

Sort the array using the function.

a := []int{3, 2, 1, 5, 4}
b := array.Sort(a, func(i, j int) bool { return a[i] < a[j] })

fmt.Println(b) // [1 2 3 4 5]
array.GroupBy
type Itens struct {
		Name        string
		Price       float64
		Description string
		Qty         int
	}

	itens := []Itens{
		{"Item 1", 10.0, "Description 1", 1},
		{"Item 2", 20.0, "Description 2", 2},
		{"Item 3", 30.0, "Description 3", 3},
		{"Item 4", 40.0, "Description 4", 10},
		{"Item 4", 40.0, "Description 4", 15},
		{"Item 4", 40.0, "Description 4", 25},
	}

	grouped := array.GroupBy(itens, func(item Itens) string {
		return fmt.Sprintf("%s - %v", item.Name, item.Price)
	})
	fmt.Println(len(grouped)) // 4
array.GroupSumBy

Group items by a key and sum a numeric value for each group.

type Itens struct {
	Name        string
	Price       float64
	Description string
	Qty         int
}

itens := []Itens{
	{"Item 1", 10.0, "Description 1", 1},
	{"Item 2", 20.0, "Description 2", 2},
	{"Item 3", 30.0, "Description 3", 3},
	{"Item 4", 40.0, "Description 4", 10},
	{"Item 4", 40.0, "Description 4", 15},
	{"Item 4", 40.0, "Description 4", 25},
}

priceByName := array.GroupSumBy(itens,
	func(item Itens) string { return item.Name },
	func(item Itens) float64 { return item.Price },
)

qtyByName := array.GroupSumBy(itens,
	func(item Itens) string { return item.Name },
	func(item Itens) int { return item.Qty },
)

fmt.Println(priceByName["Item 4"]) // 120
fmt.Println(qtyByName["Item 4"])   // 50
array.GroupSumByWhere

Filter, group and sum in one pass.

priceByName := array.GroupSumByWhere(itens,
	func(item Itens) bool { return item.Qty > 3 },
	func(item Itens) string { return item.Name },
	func(item Itens) float64 { return item.Price },
)

fmt.Println(priceByName["Item 4"]) // 120
array.GroupCountBy

Count rows by a key.

countByName := array.GroupCountBy(itens, func(item Itens) string {
	return item.Name
})

fmt.Println(countByName["Item 4"]) // 3
array.GroupReduceBy

Build custom summaries by group.

type Summary struct {
	TotalPrice float64
	TotalQty   int
}

summaryByName := array.GroupReduceBy(itens,
	func(item Itens) string {
		return item.Name
	},
	func(acc Summary, item Itens) Summary {
		acc.TotalPrice += item.Price
		acc.TotalQty += item.Qty
		return acc
	},
)

fmt.Println(summaryByName["Item 4"]) // {120 50}
array.GroupStatsBy

Calculate count, sum, min, max and average by group.

statsByName := array.GroupStatsBy(itens,
	func(item Itens) string { return item.Name },
	func(item Itens) float64 { return item.Price },
)

fmt.Println(statsByName["Item 4"].Count) // 3
fmt.Println(statsByName["Item 4"].Sum)   // 120
fmt.Println(statsByName["Item 4"].Avg)   // 40
array.DistinctBy

Keep the first row for each key.

uniqueByName := array.DistinctBy(itens, func(item Itens) string {
	return item.Name
})

fmt.Println(len(uniqueByName)) // 4
array.IndexBy

Create a map by key. If a key repeats, the last row wins.

itemByName := array.IndexBy(itens, func(item Itens) string {
	return item.Name
})

fmt.Println(itemByName["Item 4"].Qty) // 25
array.Partition

Split rows into matched and unmatched slices.

highQty, lowQty := array.Partition(itens, func(item Itens) bool {
	return item.Qty > 3
})

fmt.Println(len(highQty)) // 3
fmt.Println(len(lowQty))  // 3
array.SortBy

Sort rows by a selected field without mutating the original slice.

byQty := array.SortBy(itens, func(item Itens) int {
	return item.Qty
})

fmt.Println(byQty[0].Qty) // 1
array.Take, array.Skip, array.Chunk

Use these helpers for pagination and batch processing.

firstPage := array.Take(itens, 2)
nextRows := array.Skip(itens, 2)
batches := array.Chunk(itens, 2)

fmt.Println(len(firstPage)) // 2
fmt.Println(len(nextRows))  // 4
fmt.Println(len(batches))   // 3

chaining functions

You can chain the functions together.

data := array.Array[int]{1, 2, 3, 4, 5, 6, 7, 8, 9, 10}

  a := data.
    Filter(func(i int) bool {
      return i%2 == 0
    }).
    Map(func(i int) int {
      return i * 2
    })

  
    fmt.Println(a) // [4 8 12 16 20]

You can also group and sum values after filtering.

type Itens struct {
	Name        string
	Price       float64
	Description string
	Qty         int
}

data := array.Array[Itens]{
	{"Item 1", 10.0, "Description 1", 1},
	{"Item 2", 20.0, "Description 2", 2},
	{"Item 3", 30.0, "Description 3", 3},
	{"Item 4", 40.0, "Description 4", 10},
	{"Item 4", 40.0, "Description 4", 15},
	{"Item 4", 40.0, "Description 4", 25},
}

priceByName := data.
	Filter(func(item Itens) bool {
		return item.Qty > 3
	}).
	GroupSumBy(
		func(item Itens) string { return item.Name },
		func(item Itens) float64 { return item.Price },
	)

fmt.Println(priceByName["Item 4"]) // 120

Some helpers are also available in chain form.

countByName := data.GroupCountBy(func(item Itens) string {
	return item.Name
})

statsByName := data.GroupStatsBy(
	func(item Itens) string { return item.Name },
	func(item Itens) float64 { return item.Price },
)

uniqueByName := data.DistinctBy(func(item Itens) string {
	return item.Name
})

highQty, lowQty := data.Partition(func(item Itens) bool {
	return item.Qty > 3
})

page := data.
	SortByFloat64(func(item Itens) float64 { return item.Price }).
	Skip(10).
	Take(10)

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