lo
samber/lo
is a Lodash-style Go library based on Go 1.18+ Generics.
This project started as an experiment with the new generics implementation. It may look like Lodash in some aspects. I used to code with the fantastic "go-funk" package, but "go-funk" uses reflection and therefore is not typesafe.
As expected, benchmarks demonstrate that generics will be much faster than implementations based on the "reflect" package. Benchmarks also show similar performance gains compared to pure for
loops. See below.
In the future, 5 to 10 helpers will overlap with those coming into the Go standard library (under package names slices
and maps
). I feel this library is legitimate and offers many more valuable abstractions.
See also:
- samber/do: A dependency injection toolkit based on Go 1.18+ Generics
- samber/mo: Monads based on Go 1.18+ Generics (Option, Result, Either...)
Why this name?
I wanted a short name, similar to "Lodash" and no Go package currently uses this name.
๐ Install
go get github.com/samber/lo@v1
This library is v1 and follows SemVer strictly.
No breaking changes will be made to exported APIs before v2.0.0.
๐ก Usage
You can import lo
using:
import (
"github.com/samber/lo"
lop "github.com/samber/lo/parallel"
)
Then use one of the helpers below:
names := lo.Uniq[string]([]string{"Samuel", "Marc", "Samuel"})
// []string{"Samuel", "Marc"}
Most of the time, the compiler will be able to infer the type so that you can call: lo.Uniq([]string{...})
.
๐ค Spec
GoDoc: https://godoc.org/github.com/samber/lo
Supported helpers for slices:
- Filter
- Map
- FilterMap
- FlatMap
- Reduce
- ForEach
- Times
- Uniq
- UniqBy
- GroupBy
- Chunk
- PartitionBy
- Flatten
- Shuffle
- Reverse
- Fill
- Repeat
- KeyBy
- Drop
- DropRight
- DropWhile
- DropRightWhile
- Reject
- Count
- CountBy
Supported helpers for maps:
- Keys
- Values
- PickBy
- PickByKeys
- PickByValues
- OmitBy
- OmitByKeys
- OmitByValues
- Entries
- FromEntries
- Invert
- Assign (merge of maps)
- MapKeys
- MapValues
Supported math helpers:
- Range / RangeFrom / RangeWithSteps
- Clamp
- SumBy
Supported helpers for strings:
- Substring
- RuneLength
Supported helpers for tuples:
- T2 -> T9
- Unpack2 -> Unpack9
- Zip2 -> Zip9
- Unzip2 -> Unzip9
Supported intersection helpers:
- Contains
- ContainsBy
- Every
- EveryBy
- Some
- SomeBy
- None
- NoneBy
- Intersect
- Difference
- Union
Supported search helpers:
- IndexOf
- LastIndexOf
- Find
- FindIndexOf
- FindLastIndexOf
- Min
- MinBy
- Max
- MaxBy
- Last
- Nth
- Sample
- Samples
Conditional helpers:
- Ternary (1 line if/else statement)
- If / ElseIf / Else
- Switch / Case / Default
Type manipulation helpers:
- ToPtr
- ToSlicePtr
- ToAnySlice
- FromAnySlice
- Empty
- Coalesce
Concurrency helpers:
- Attempt
- AttemptWithDelay
- Debounce
- Async
Error handling:
- Must
- Try
- TryCatch
- TryWithErrorValue
- TryCatchWithErrorValue
Constraints:
- Clonable
Map
Manipulates a slice of one type and transforms it into a slice of another type:
import "github.com/samber/lo"
lo.Map[int64, string]([]int64{1, 2, 3, 4}, func(x int64, _ int) string {
return strconv.FormatInt(x, 10)
})
// []string{"1", "2", "3", "4"}
Parallel processing: like lo.Map()
, but the mapper function is called in a goroutine. Results are returned in the same order.
import lop "github.com/samber/lo/parallel"
lop.Map[int64, string]([]int64{1, 2, 3, 4}, func(x int64, _ int) string {
return strconv.FormatInt(x, 10)
})
// []string{"1", "2", "3", "4"}
FlatMap
Manipulates a slice and transforms and flattens it to a slice of another type.
lo.FlatMap[int, string]([]int{0, 1, 2}, func(x int, _ int) []string {
return []string{
strconv.FormatInt(x, 10),
strconv.FormatInt(x, 10),
}
})
// []string{"0", "0", "1", "1", "2", "2"}
FilterMap
Returns a slice which obtained after both filtering and mapping using the given callback function.
The callback function should return two values: the result of the mapping operation and whether the result element should be included or not.
matching := lo.FilterMap[string, string]([]string{"cpu", "gpu", "mouse", "keyboard"}, func(x string, _ int) (string, bool) {
if strings.HasSuffix(x, "pu") {
return "xpu", true
}
return "", false
})
// []string{"xpu", "xpu"}
Filter
Iterates over a collection and returns an array of all the elements the predicate function returns true
for.
even := lo.Filter[int]([]int{1, 2, 3, 4}, func(x int, _ int) bool {
return x%2 == 0
})
// []int{2, 4}
Contains
Returns true if an element is present in a collection.
present := lo.Contains[int]([]int{0, 1, 2, 3, 4, 5}, 5)
// true
ContainsBy
Returns true if the predicate function returns true
.
present := lo.ContainsBy[int]([]int{0, 1, 2, 3, 4, 5}, func(x int) bool {
return x == 3
})
// true
Reduce
Reduces a collection to a single value. The value is calculated by accumulating the result of running each element in the collection through an accumulator function. Each successive invocation is supplied with the return value returned by the previous call.
sum := lo.Reduce[int, int]([]int{1, 2, 3, 4}, func(agg int, item int, _ int) int {
return agg + item
}, 0)
// 10
ForEach
Iterates over elements of a collection and invokes the function over each element.
import "github.com/samber/lo"
lo.ForEach[string]([]string{"hello", "world"}, func(x string, _ int) {
println(x)
})
// prints "hello\nworld\n"
Parallel processing: like lo.ForEach()
, but the callback is called as a goroutine.
import lop "github.com/samber/lo/parallel"
lop.ForEach[string]([]string{"hello", "world"}, func(x string, _ int) {
println(x)
})
// prints "hello\nworld\n" or "world\nhello\n"
Times
Times invokes the iteratee n times, returning an array of the results of each invocation. The iteratee is invoked with index as argument.
import "github.com/samber/lo"
lo.Times[string](3, func(i int) string {
return strconv.FormatInt(int64(i), 10)
})
// []string{"0", "1", "2"}
Parallel processing: like lo.Times()
, but callback is called in goroutine.
import lop "github.com/samber/lo/parallel"
lop.Times[string](3, func(i int) string {
return strconv.FormatInt(int64(i), 10)
})
// []string{"0", "1", "2"}
Uniq
Returns a duplicate-free version of an array, in which only the first occurrence of each element is kept. The order of result values is determined by the order they occur in the array.
uniqValues := lo.Uniq[int]([]int{1, 2, 2, 1})
// []int{1, 2}
UniqBy
Returns a duplicate-free version of an array, in which only the first occurrence of each element is kept. The order of result values is determined by the order they occur in the array. It accepts iteratee
which is invoked for each element in array to generate the criterion by which uniqueness is computed.
uniqValues := lo.UniqBy[int, int]([]int{0, 1, 2, 3, 4, 5}, func(i int) int {
return i%3
})
// []int{0, 1, 2}
GroupBy
Returns an object composed of keys generated from the results of running each element of collection through iteratee.
import lo "github.com/samber/lo"
groups := lo.GroupBy[int, int]([]int{0, 1, 2, 3, 4, 5}, func(i int) int {
return i%3
})
// map[int][]int{0: []int{0, 3}, 1: []int{1, 4}, 2: []int{2, 5}}
Parallel processing: like lo.GroupBy()
, but callback is called in goroutine.
import lop "github.com/samber/lo/parallel"
lop.GroupBy[int, int]([]int{0, 1, 2, 3, 4, 5}, func(i int) int {
return i%3
})
// map[int][]int{0: []int{0, 3}, 1: []int{1, 4}, 2: []int{2, 5}}
Chunk
Returns an array of elements split into groups the length of size. If array can't be split evenly, the final chunk will be the remaining elements.
lo.Chunk[int]([]int{0, 1, 2, 3, 4, 5}, 2)
// [][]int{{0, 1}, {2, 3}, {4, 5}}
lo.Chunk[int]([]int{0, 1, 2, 3, 4, 5, 6}, 2)
// [][]int{{0, 1}, {2, 3}, {4, 5}, {6}}
lo.Chunk[int]([]int{}, 2)
// [][]int{}
lo.Chunk[int]([]int{0}, 2)
// [][]int{{0}}
PartitionBy
Returns an array of elements split into groups. The order of grouped values is determined by the order they occur in collection. The grouping is generated from the results of running each element of collection through iteratee.
import lo "github.com/samber/lo"
partitions := lo.PartitionBy[int, string]([]int{-2, -1, 0, 1, 2, 3, 4, 5}, func(x int) string {
if x < 0 {
return "negative"
} else if x%2 == 0 {
return "even"
}
return "odd"
})
// [][]int{{-2, -1}, {0, 2, 4}, {1, 3, 5}}
Parallel processing: like lo.PartitionBy()
, but callback is called in goroutine. Results are returned in the same order.
import lop "github.com/samber/lo/parallel"
partitions := lo.PartitionBy[int, string]([]int{-2, -1, 0, 1, 2, 3, 4, 5}, func(x int) string {
if x < 0 {
return "negative"
} else if x%2 == 0 {
return "even"
}
return "odd"
})
// [][]int{{-2, -1}, {0, 2, 4}, {1, 3, 5}}
Flatten
Returns an array a single level deep.
flat := lo.Flatten[int]([][]int{{0, 1}, {2, 3, 4, 5}})
// []int{0, 1, 2, 3, 4, 5}
Shuffle
Returns an array of shuffled values. Uses the Fisher-Yates shuffle algorithm.
randomOrder := lo.Shuffle[int]([]int{0, 1, 2, 3, 4, 5})
// []int{0, 1, 2, 3, 4, 5}
Reverse
Reverses array so that the first element becomes the last, the second element becomes the second to last, and so on.
reverseOder := lo.Reverse[int]([]int{0, 1, 2, 3, 4, 5})
// []int{5, 4, 3, 2, 1, 0}
Fill
Fills elements of array with initial
value.
type foo struct {
bar string
}
func (f foo) Clone() foo {
return foo{f.bar}
}
initializedSlice := lo.Fill[foo]([]foo{foo{"a"}, foo{"a"}}, foo{"b"})
// []foo{foo{"b"}, foo{"b"}}
Repeat
Builds a slice with N copies of initial value.
type foo struct {
bar string
}
func (f foo) Clone() foo {
return foo{f.bar}
}
slice := lo.Repeat[foo](2, foo{"a"})
// []foo{foo{"a"}, foo{"a"}}
RepeatBy
Builds a slice with values returned by N calls of callback.
slice := lo.RepeatBy[int](0, func (i int) int {
return math.Pow(i, 2)
})
// []int{}
slice := lo.RepeatBy[int](5, func (i int) int {
return math.Pow(i, 2)
})
// []int{0, 1, 4, 9, 16}
KeyBy
Transforms a slice or an array of structs to a map based on a pivot callback.
m := lo.KeyBy[int, string]([]string{"a", "aa", "aaa"}, func(str string) int {
return len(str)
})
// map[int]string{1: "a", 2: "aa", 3: "aaa"}
type Character struct {
dir string
code int
}
characters := []Character{
{dir: "left", code: 97},
{dir: "right", code: 100},
}
result := lo.KeyBy[string, Character](characters, func(char Character) string {
return string(rune(char.code))
})
//map[a:{dir:left code:97} d:{dir:right code:100}]
Drop
Drops n elements from the beginning of a slice or array.
l := lo.Drop[int]([]int{0, 1, 2, 3, 4, 5}, 2)
// []int{2, 3, 4, 5}
DropRight
Drops n elements from the end of a slice or array.
l := lo.DropRight[int]([]int{0, 1, 2, 3, 4, 5}, 2)
// []int{0, 1, 2, 3}
DropWhile
Drop elements from the beginning of a slice or array while the predicate returns true.
l := lo.DropWhile[string]([]string{"a", "aa", "aaa", "aa", "aa"}, func(val string) bool {
return len(val) <= 2
})
// []string{"aaa", "aa", "aa"}
DropRightWhile
Drop elements from the end of a slice or array while the predicate returns true.
l := lo.DropRightWhile[string]([]string{"a", "aa", "aaa", "aa", "aa"}, func(val string) bool {
return len(val) <= 2
})
// []string{"a", "aa", "aaa"}
Reject
The opposite of Filter, this method returns the elements of collection that predicate does not return truthy for.
odd := lo.Reject[int]([]int{1, 2, 3, 4}, func(x int, _ int) bool {
return x%2 == 0
})
// []int{1, 3}
Count
Counts the number of elements in the collection that compare equal to value.
count := lo.Count[int]([]int{1, 5, 1}, 1)
// 2
CountBy
Counts the number of elements in the collection for which predicate is true.
count := lo.CountBy[int]([]int{1, 5, 1}, func(i int) bool {
return i < 4
})
// 2
Subset
Return part of a slice.
in := []int{0, 1, 2, 3, 4}
sub := lo.Subset(in, 2, 3)
// []int{2, 3, 4}
sub := lo.Subset(in, -4, 3)
// []int{1, 2, 3}
sub := lo.Subset(in, -2, math.MaxUint)
// []int{3, 4}
Replace
Returns a copy of the slice with the first n non-overlapping instances of old replaced by new.
in := []int{0, 1, 0, 1, 2, 3, 0}
slice := lo.Replace(in, 0, 42, 1)
// []int{42, 1, 0, 1, 2, 3, 0}
slice := lo.Replace(in, -1, 42, 1)
// []int{0, 1, 0, 1, 2, 3, 0}
slice := lo.Replace(in, 0, 42, 2)
// []int{42, 1, 42, 1, 2, 3, 0}
slice := lo.Replace(in, 0, 42, -1)
// []int{42, 1, 42, 1, 2, 3, 42}
ReplaceAll
Returns a copy of the slice with all non-overlapping instances of old replaced by new.
in := []int{0, 1, 0, 1, 2, 3, 0}
slice := lo.ReplaceAll(in, 0, 42)
// []int{42, 1, 42, 1, 2, 3, 42}
slice := lo.ReplaceAll(in, -1, 42)
// []int{0, 1, 0, 1, 2, 3, 0}
Keys
Creates an array of the map keys.
keys := lo.Keys[string, int](map[string]int{"foo": 1, "bar": 2})
// []string{"bar", "foo"}
Values
Creates an array of the map values.
values := lo.Values[string, int](map[string]int{"foo": 1, "bar": 2})
// []int{1, 2}
PickBy
Returns same map type filtered by given predicate.
m := lo.PickBy[string, int](map[string]int{"foo": 1, "bar": 2, "baz": 3}, func(key string, value int) bool {
return value%2 == 1
})
// map[string]int{"foo": 1, "baz": 3}
PickByKeys
Returns same map type filtered by given keys.
m := lo.PickByKeys[string, int](map[string]int{"foo": 1, "bar": 2, "baz": 3}, []string{"foo", "baz"})
// map[string]int{"foo": 1, "baz": 3}
PickByValues
Returns same map type filtered by given values.
m := lo.PickByValues[string, int](map[string]int{"foo": 1, "bar": 2, "baz": 3}, []int{1, 3})
// map[string]int{"foo": 1, "baz": 3}
OmitBy
Returns same map type filtered by given predicate.
m := lo.OmitBy[string, int](map[string]int{"foo": 1, "bar": 2, "baz": 3}, func(key string, value int) bool {
return value%2 == 1
})
// map[string]int{"bar": 2}
OmitByKeys
Returns same map type filtered by given keys.
m := lo.OmitByKeys[string, int](map[string]int{"foo": 1, "bar": 2, "baz": 3}, []string{"foo", "baz"})
// map[string]int{"bar": 2}
OmitByValues
Returns same map type filtered by given values.
m := lo.OmitByValues[string, int](map[string]int{"foo": 1, "bar": 2, "baz": 3}, []int{1, 3})
// map[string]int{"bar": 2}
Entries
Transforms a map into array of key/value pairs.
entries := lo.Entries[string, int](map[string]int{"foo": 1, "bar": 2})
// []lo.Entry[string, int]{
// {
// Key: "foo",
// Value: 1,
// },
// {
// Key: "bar",
// Value: 2,
// },
// }
FromEntries
Transforms an array of key/value pairs into a map.
m := lo.FromEntries[string, int]([]lo.Entry[string, int]{
{
Key: "foo",
Value: 1,
},
{
Key: "bar",
Value: 2,
},
})
// map[string]int{"foo": 1, "bar": 2}
Invert
Creates a map composed of the inverted keys and values. If map contains duplicate values, subsequent values overwrite property assignments of previous values.
m1 := lo.Invert[string, int]([map[string]int{"a": 1, "b": 2})
// map[int]string{1: "a", 2: "b"}
m2 := lo.Invert[string, int]([map[string]int{"a": 1, "b": 2, "c": 1})
// map[int]string{1: "c", 2: "b"}
Assign
Merges multiple maps from left to right.
mergedMaps := lo.Assign[string, int](
map[string]int{"a": 1, "b": 2},
map[string]int{"b": 3, "c": 4},
)
// map[string]int{"a": 1, "b": 3, "c": 4}
MapKeys
Manipulates a map keys and transforms it to a map of another type.
m2 := lo.MapKeys[int, int, string](map[int]int{1: 1, 2: 2, 3: 3, 4: 4}, func(_ int, v int) string {
return strconv.FormatInt(int64(v), 10)
})
// map[string]int{"1": 1, "2": 2, "3": 3, "4": 4}
MapValues
Manipulates a map values and transforms it to a map of another type.
m1 := map[int]int64{1: 1, 2: 2, 3: 3}
m2 := lo.MapValues[int, int64, string](m1, func(x int64, _ int) string {
return strconv.FormatInt(x, 10)
})
// map[int]string{1: "1", 2: "2", 3: "3"}
Range / RangeFrom / RangeWithSteps
Creates an array of numbers (positive and/or negative) progressing from start up to, but not including end.
result := Range(4)
// [0, 1, 2, 3]
result := Range(-4);
// [0, -1, -2, -3]
result := RangeFrom(1, 5);
// [1, 2, 3, 4]
result := RangeFrom[float64](1.0, 5);
// [1.0, 2.0, 3.0, 4.0]
result := RangeWithSteps(0, 20, 5);
// [0, 5, 10, 15]
result := RangeWithSteps[float32](-1.0, -4.0, -1.0);
// [-1.0, -2.0, -3.0]
result := RangeWithSteps(1, 4, -1);
// []
result := Range(0);
// []
Clamp
Clamps number within the inclusive lower and upper bounds.
r1 := lo.Clamp(0, -10, 10)
// 0
r2 := lo.Clamp(-42, -10, 10)
// -10
r3 := lo.Clamp(42, -10, 10)
// 10
SumBy
Summarizes the values in a collection using the given return value from the iteration function. If collection is empty 0 is returned.
strings := []string{"foo", "bar"}
sum := lo.SumBy(strings, func(item string) int {
return len(item)
})
// 6
Substring
Return part of a string.
sub := lo.Substring("hello", 2, 3)
// "llo"
sub := lo.Substring("hello", -4, 3)
// "ell"
sub := lo.Substring("hello", -2, math.MaxUint)
// "lo"
RuneLength
An alias to utf8.RuneCountInString which returns the number of runes in string.
sub := lo.RuneLength("hellรด")
// 5
sub := len("hellรด")
// 6
T2 -> T9
Creates a tuple from a list of values.
tuple1 := lo.T2[string, int]("x", 1)
// Tuple2[string, int]{A: "x", B: 1}
func example() (string, int) { return "y", 2 }
tuple2 := lo.T2[string, int](example())
// Tuple2[string, int]{A: "y", B: 2}
Unpack2 -> Unpack9
Returns values contained in tuple.
r1, r2 := lo.Unpack2[string, int](lo.Tuple2[string, int]{"a", 1})
// "a", 1
Zip2 -> Zip9
Zip creates a slice of grouped elements, the first of which contains the first elements of the given arrays, the second of which contains the second elements of the given arrays, and so on.
When collections have different size, the Tuple attributes are filled with zero value.
tuples := lo.Zip2[string, int]([]string{"a", "b"}, []int{1, 2})
// []Tuple2[string, int]{{A: "a", B: 1}, {A: "b", B: 2}}
Unzip2 -> Unzip9
Unzip accepts an array of grouped elements and creates an array regrouping the elements to their pre-zip configuration.
a, b := lo.Unzip2[string, int]([]Tuple2[string, int]{{A: "a", B: 1}, {A: "b", B: 2}})
// []string{"a", "b"}
// []int{1, 2}
Every
Returns true if all elements of a subset are contained into a collection or if the subset is empty.
ok := lo.Every[int]([]int{0, 1, 2, 3, 4, 5}, []int{0, 2})
// true
ok := lo.Every[int]([]int{0, 1, 2, 3, 4, 5}, []int{0, 6})
// false
EveryBy
Returns true if the predicate returns true for all of the elements in the collection or if the collection is empty.
b := EveryBy[int]([]int{1, 2, 3, 4}, func(x int) bool {
return x < 5
})
// true
Some
Returns true if at least 1 element of a subset is contained into a collection. If the subset is empty Some returns false.
ok := lo.Some[int]([]int{0, 1, 2, 3, 4, 5}, []int{0, 2})
// true
ok := lo.Some[int]([]int{0, 1, 2, 3, 4, 5}, []int{-1, 6})
// false
SomeBy
Returns true if the predicate returns true for any of the elements in the collection. If the collection is empty SomeBy returns false.
b := SomeBy[int]([]int{1, 2, 3, 4}, func(x int) bool {
return x < 3
})
// true
None
Returns true if no element of a subset are contained into a collection or if the subset is empty.
b := None[int]([]int{0, 1, 2, 3, 4, 5}, []int{0, 2})
// false
b := None[int]([]int{0, 1, 2, 3, 4, 5}, []int{-1, 6})
// true
NoneBy
Returns true if the predicate returns true for none of the elements in the collection or if the collection is empty.
b := NoneBy[int]([]int{1, 2, 3, 4}, func(x int) bool {
return x < 0
})
// true
Intersect
Returns the intersection between two collections.
result1 := lo.Intersect[int]([]int{0, 1, 2, 3, 4, 5}, []int{0, 2})
// []int{0, 2}
result2 := lo.Intersect[int]([]int{0, 1, 2, 3, 4, 5}, []int{0, 6}
// []int{0}
result3 := lo.Intersect[int]([]int{0, 1, 2, 3, 4, 5}, []int{-1, 6})
// []int{}
Difference
Returns the difference between two collections.
- The first value is the collection of element absent of list2.
- The second value is the collection of element absent of list1.
left, right := lo.Difference[int]([]int{0, 1, 2, 3, 4, 5}, []int{0, 2, 6})
// []int{1, 3, 4, 5}, []int{6}
left, right := lo.Difference[int]([]int{0, 1, 2, 3, 4, 5}, []int{0, 1, 2, 3, 4, 5})
// []int{}, []int{}
Union
Returns all distinct elements from both collections. Result will not change the order of elements relatively.
union := lo.Union[int]([]int{0, 1, 2, 3, 4, 5}, []int{0, 2, 10})
// []int{0, 1, 2, 3, 4, 5, 10}
IndexOf
Returns the index at which the first occurrence of a value is found in an array or return -1 if the value cannot be found.
found := lo.IndexOf[int]([]int{0, 1, 2, 1, 2, 3}, 2)
// 2
notFound := lo.IndexOf[int]([]int{0, 1, 2, 1, 2, 3}, 6)
// -1
LastIndex
Returns the index at which the last occurrence of a value is found in an array or return -1 if the value cannot be found.
found := lo.LastIndexOf[int]([]int{0, 1, 2, 1, 2, 3}, 2)
// 4
notFound := lo.LastIndexOf[int]([]int{0, 1, 2, 1, 2, 3}, 6)
// -1
Find
Search an element in a slice based on a predicate. It returns element and true if element was found.
str, ok := lo.Find[string]([]string{"a", "b", "c", "d"}, func(i string) bool {
return i == "b"
})
// "b", true
str, ok := lo.Find[string]([]string{"foobar"}, func(i string) bool {
return i == "b"
})
// "", false
FindIndexOf
FindIndexOf searches an element in a slice based on a predicate and returns the index and true. It returns -1 and false if the element is not found.
str, index, ok := lo.FindIndexOf[string]([]string{"a", "b", "a", "b"}, func(i string) bool {
return i == "b"
})
// "b", 1, true
str, index, ok := lo.FindIndexOf[string]([]string{"foobar"}, func(i string) bool {
return i == "b"
})
// "", -1, false
FindLastIndexOf
FindLastIndexOf searches an element in a slice based on a predicate and returns the index and true. It returns -1 and false if the element is not found.
str, index, ok := lo.FindLastIndexOf[string]([]string{"a", "b", "a", "b"}, func(i string) bool {
return i == "b"
})
// "b", 4, true
str, index, ok := lo.FindLastIndexOf[string]([]string{"foobar"}, func(i string) bool {
return i == "b"
})
// "", -1, false
Min
Search the minimum value of a collection.
min := lo.Min[int]([]int{1, 2, 3})
// 1
min := lo.Min[int]([]int{})
// 0
MinBy
Search the minimum value of a collection using the given comparison function. If several values of the collection are equal to the smallest value, returns the first such value.
min := lo.MinBy[string]([]string{"s1", "string2", "s3"}, func(item string, min string) bool {
return len(item) < len(min)
})
// "s1"
min := lo.MinBy[string]([]string{}, func(item string, min string) bool {
return len(item) < len(min)
})
// ""
Max
Search the maximum value of a collection.
max := lo.Max[int]([]int{1, 2, 3})
// 3
max := lo.Max[int]([]int{})
// 0
MaxBy
Search the maximum value of a collection using the given comparison function. If several values of the collection are equal to the greatest value, returns the first such value.
max := lo.MaxBy[string]([]string{"string1", "s2", "string3"}, func(item string, max string) bool {
return len(item) > len(max)
})
// "string1"
max := lo.MaxBy[string]([]string{}, func(item string, max string) bool {
return len(item) > len(max)
})
// ""
Last
Returns the last element of a collection or error if empty.
last, err := lo.Last[int]([]int{1, 2, 3})
// 3
Nth
Returns the element at index nth
of collection. If nth
is negative, the nth element from the end is returned. An error is returned when nth is out of slice bounds.
nth, err := lo.Nth[int]([]int{0, 1, 2, 3}, 2)
// 2
nth, err := lo.Nth[int]([]int{0, 1, 2, 3}, -2)
// 2
Sample
Returns a random item from collection.
lo.Sample[string]([]string{"a", "b", "c"})
// a random string from []string{"a", "b", "c"}
lo.Sample[string]([]string{})
// ""
Samples
Returns N random unique items from collection.
lo.Samples[string]([]string{"a", "b", "c"}, 3)
// []string{"a", "b", "c"} in random order
Ternary
A 1 line if/else statement.
result := lo.Ternary[string](true, "a", "b")
// "a"
result := lo.Ternary[string](false, "a", "b")
// "b"
If / ElseIf / Else
result := lo.If[int](true, 1).
ElseIf(false, 2).
Else(3)
// 1
result := lo.If[int](false, 1).
ElseIf(true, 2).
Else(3)
// 2
result := lo.If[int](false, 1).
ElseIf(false, 2).
Else(3)
// 3
Using callbacks:
result := lo.IfF[int](true, func () int {
return 1
}).
ElseIfF(false, func () int {
return 2
}).
ElseF(func () int {
return 3
})
// 1
Mixed:
result := lo.IfF[int](true, func () int {
return 1
}).
Else(42)
// 1
Switch / Case / Default
result := lo.Switch[int, string](1).
Case(1, "1").
Case(2, "2").
Default("3")
// "1"
result := lo.Switch[int, string](2).
Case(1, "1").
Case(2, "2").
Default("3")
// "2"
result := lo.Switch[int, string](42).
Case(1, "1").
Case(2, "2").
Default("3")
// "3"
Using callbacks:
result := lo.Switch[int, string](1).
CaseF(1, func() string {
return "1"
}).
CaseF(2, func() string {
return "2"
}).
DefaultF(func() string {
return "3"
})
// "1"
Mixed:
result := lo.Switch[int, string](1).
CaseF(1, func() string {
return "1"
}).
Default("42")
// "1"
ToPtr
Returns a pointer copy of value.
ptr := lo.ToPtr[string]("hello world")
// *string{"hello world"}
ToSlicePtr
Returns a slice of pointer copy of value.
ptr := lo.ToSlicePtr[string]([]string{"hello", "world"})
// []*string{"hello", "world"}
ToAnySlice
Returns a slice with all elements mapped to any
type.
elements := lo.ToAnySlice[int]([]int{1, 5, 1})
// []any{1, 5, 1}
FromAnySlice
Returns an any
slice with all elements mapped to a type. Returns false in case of type conversion failure.
elements, ok := lo.FromAnySlice[string]([]any{"foobar", 42})
// []string{}, false
elements, ok := lo.FromAnySlice[string]([]any{"foobar", "42"})
// []string{"foobar", "42"}, true
Empty
Returns an empty value.
lo.Empty[int]()
// 0
lo.Empty[string]()
// ""
lo.Empty[bool]()
// false
Coalesce
Returns the first non-empty arguments. Arguments must be comparable.
result, ok := lo.Coalesce(0, 1, 2, 3)
// 1 true
result, ok := lo.Coalesce("")
// "" false
var nilStr *string
str := "foobar"
result, ok := lo.Coalesce[*string](nil, nilStr, &str)
// &"foobar" true
Attempt
Invokes a function N times until it returns valid output. Returning either the caught error or nil. When first argument is less than 1
, the function runs until a sucessfull response is returned.
iter, err := lo.Attempt(42, func(i int) error {
if i == 5 {
return nil
}
return fmt.Errorf("failed")
})
// 6
// nil
iter, err := lo.Attempt(2, func(i int) error {
if i == 5 {
return nil
}
return fmt.Errorf("failed")
})
// 2
// error "failed"
iter, err := lo.Attempt(0, func(i int) error {
if i < 42 {
return fmt.Errorf("failed")
}
return nil
})
// 43
// nil
For more advanced retry strategies (delay, exponential backoff...), please take a look on cenkalti/backoff.
AttemptWithDelay
Invokes a function N times until it returns valid output, with a pause betwwen each call. Returning either the caught error or nil.
When first argument is less than 1
, the function runs until a sucessfull response is returned.
iter, duration, err := lo.AttemptWithDelay(5, 2*time.Second, func(i int, duration time.Duration) error {
if i == 2 {
return nil
}
return fmt.Errorf("failed")
})
// 3
// ~ 4 seconds
// nil
For more advanced retry strategies (delay, exponential backoff...), please take a look on cenkalti/backoff.
Debounce
NewDebounce
creates a debounced instance that delays invoking functions given until after wait milliseconds have elapsed, until cancel
is called.
f := func() {
println("Called once after 100ms when debounce stopped invoking!")
}
debounce, cancel := lo.NewDebounce(100 * time.Millisecond, f)
for j := 0; j < 10; j++ {
debounce()
}
time.Sleep(1 * time.Second)
cancel()
Synchronize
Wraps the underlying callback in a mutex. It receives an optional mutex.
s := lo.Synchronize()
for i := 0; i < 10; i++ {
go s.Do(func () {
println("will be called sequentially")
})
}
It is equivalent to:
mu := sync.Mutex{}
func foobar() {
mu.Lock()
defer mu.Unlock()
// ...
}
Async
Executes a function in a goroutine and returns the result in a channel.
ch := lo.Async(func() error { time.Sleep(10 * time.Second); return nil })
// chan error (nil)
Async{0->6}
Executes a function in a goroutine and returns the result in a channel. For function with multiple return values, the results will be returned as a tuple inside the channel. For function without return, struct{} will be returned in the channel.
ch := lo.Async0(func() { time.Sleep(10 * time.Second) })
// chan struct{}
ch := lo.Async1(func() int {
time.Sleep(10 * time.Second);
return 42
})
// chan int (42)
ch := lo.Async2(func() (int, string) {
time.Sleep(10 * time.Second);
return 42, "Hello"
})
// chan lo.Tuple2[int, string] ({42, "Hello"})
Must
Wraps a function call to panics if second argument is error
or false
, returns the value otherwise.
val := lo.Must(time.Parse("2006-01-02", "2022-01-15"))
// 2022-01-15
val := lo.Must(time.Parse("2006-01-02", "bad-value"))
// panics
Must{0->6}
Must* has the same behavior than Must, but returns multiple values.
func example0() (error)
func example1() (int, error)
func example2() (int, string, error)
func example3() (int, string, time.Date, error)
func example4() (int, string, time.Date, bool, error)
func example5() (int, string, time.Date, bool, float64, error)
func example6() (int, string, time.Date, bool, float64, byte, error)
lo.Must0(example0())
val1 := lo.Must1(example1()) // alias to Must
val1, val2 := lo.Must2(example2())
val1, val2, val3 := lo.Must3(example3())
val1, val2, val3, val4 := lo.Must4(example4())
val1, val2, val3, val4, val5 := lo.Must5(example5())
val1, val2, val3, val4, val5, val6 := lo.Must6(example6())
You can wrap functions like func (...) (..., ok bool)
.
// math.Signbit(float64) bool
lo.Must0(math.Signbit(v))
// bytes.Cut([]byte,[]byte) ([]byte, []byte, bool)
before, after := lo.Must2(bytes.Cut(s, sep))
Try
Calls the function and return false in case of error and on panic.
ok := lo.Try(func() error {
panic("error")
return nil
})
// false
ok := lo.Try(func() error {
return nil
})
// true
ok := lo.Try(func() error {
return fmt.Errorf("error")
})
// false
Try{0->6}
The same behavior than Try
, but callback returns 2 variables.
ok := lo.Try2(func() (string, error) {
panic("error")
return "", nil
})
// false
TryWithErrorValue
The same behavior than Try
, but also returns value passed to panic.
err, ok := lo.TryWithErrorValue(func() error {
panic("error")
return nil
})
// "error", false
TryCatch
The same behavior than Try
, but calls the catch function in case of error.
caught := false
ok := lo.TryCatch(func() error {
panic("error")
return nil
}, func() {
caught = true
})
// false
// caught == true
TryCatchWithErrorValue
The same behavior than TryWithErrorValue
, but calls the catch function in case of error.
caught := false
ok := lo.TryCatchWithErrorValue(func() error {
panic("error")
return nil
}, func(val any) {
caught = val == "error"
})
// false
// caught == true
๐ฉ Benchmark
We executed a simple benchmark with the a dead-simple lo.Map
loop:
See the full implementation here.
_ = lo.Map[int64](arr, func(x int64, i int) string {
return strconv.FormatInt(x, 10)
})
Result:
Here is a comparison between lo.Map
, lop.Map
, go-funk
library and a simple Go for
loop.
$ go test -benchmem -bench ./...
goos: linux
goarch: amd64
pkg: github.com/samber/lo
cpu: Intel(R) Core(TM) i5-7267U CPU @ 3.10GHz
cpu: Intel(R) Core(TM) i7 CPU 920 @ 2.67GHz
BenchmarkMap/lo.Map-8 8 132728237 ns/op 39998945 B/op 1000002 allocs/op
BenchmarkMap/lop.Map-8 2 503947830 ns/op 119999956 B/op 3000007 allocs/op
BenchmarkMap/reflect-8 2 826400560 ns/op 170326512 B/op 4000042 allocs/op
BenchmarkMap/for-8 9 126252954 ns/op 39998674 B/op 1000001 allocs/op
PASS
ok github.com/samber/lo 6.657s
lo.Map
is way faster (x7) thango-funk
, a relection-based Map implementation.lo.Map
have the same allocation profile thanfor
.lo.Map
is 4% slower thanfor
.lop.Map
is slower thanlo.Map
because it implies more memory allocation and locks.lop.Map
will be usefull for long-running callbacks, such as i/o bound processing.for
beats other implementations for memory and CPU.
๐ค Contributing
- Ping me on twitter @samuelberthe (DMs, mentions, whatever :))
- Fork the project
- Fix open issues or request new features
Don't hesitate ;)
Install go 1.18
make go1.18beta1
If your OS currently not default to Go 1.18, replace BIN=go
by BIN=go1.18beta1
in the Makefile.
With Docker
docker-compose run --rm dev
Without Docker
# Install some dev dependencies
make tools
# Run tests
make test
# or
make watch-test
๐ค Authors
- Samuel Berthe
๐ซ Show your support
Give a
๐ License
Copyright ยฉ 2022 Samuel Berthe.
This project is MIT licensed.