add group by to docs

Makefile

@@ -14,6 +14,7 @@ scan:
 scan-config:
 	trivy config .
 
+.PHONY: docs
 docs:
 	cd docs && hugo server -D
 

docs/content/_index.md

@@ -9,10 +9,9 @@ title: _Underscore
 
 ![underscore](https://socialify.git.ci/rjNemo/underscore/image?description=1&font=KoHo&language=1&logo=https%3A%2F%2Fraw.githubusercontent.com%2FrjNemo%2Funderscore%2Fmain%2Fdocs%2Fstatic%2Flogo.png&owner=1&pattern=Floating%20Cogs&stargazers=1&theme=Dark)
 
-
 `underscore` is a `Go` library providing useful functional programming helpers without extending any built-in objects.
 
-It is mostly a port from the `underscore.js` library based on generics brought by `go1.18`.
+It is mostly a port from the `underscore.js` library based on generics available from `go1.18`.
 
 ## Quick Start
 

docs/content/collections/groupby.md

@@ -0,0 +1,21 @@
+---
+title: "Group by"
+date: 2023-06-07T00:49:56+02:00
+---
+
+GroupBy splits a slice into a map[K][]V grouped by the result of the iterator function.
+
+```go
+package main
+
+import (
+	"fmt"
+	u "github.com/rjNemo/underscore"
+)
+
+func main() {
+  	nums := []float64{1.3, 2.1, 2.4}
+	groupingFunc := func(n float64) int { return int(math.Floor(n)) }
+  	res := u.GroupBy(nums, groupingFunc) // { 1: {1.3}, 2: {2.1, 2.4}}
+}
+```