Implement NextTo and PrevTo on iterator

README.md

@@ -983,6 +983,22 @@ for it.Begin(); it.Next(); {
 }
 ```
 
+Seeking to a specific element:
+
+```go
+// Seek function, i.e. find element starting with "b"
+seek := func(index int, value interface{}) bool {
+    return strings.HasSuffix(value.(string), "b")
+}
+
+// Seek to the condition and continue traversal from that point (forward).
+// assumes it.Begin() was called.
+for found := it.NextTo(seek); found; found = it.Next() {
+    index, value := it.Index(), it.Value()
+    ...
+}
+```
+
 #### IteratorWithKey
 
 An [iterator](#iterator) whose elements are referenced by a key.
@@ -1010,6 +1026,22 @@ for it.Begin(); it.Next(); {
 }
 ```
 
+Seeking to a specific element from the current iterator position:
+
+```go
+// Seek function, i.e. find element starting with "b"
+seek := func(key interface{}, value interface{}) bool {
+    return strings.HasSuffix(value.(string), "b")
+}
+
+// Seek to the condition and continue traversal from that point (forward).
+// assumes it.Begin() was called.
+for found := it.NextTo(seek); found; found = it.Next() {
+    key, value := it.Key(), it.Value()
+    ...
+}
+```
+
 #### ReverseIteratorWithIndex
 
 An [iterator](#iterator) whose elements are referenced by an index. Provides all functions as [IteratorWithIndex](#iteratorwithindex), but can also be used for reverse iteration.
@@ -1031,6 +1063,22 @@ if it.Last() {
 }
 ```
 
+Seeking to a specific element:
+
+```go
+// Seek function, i.e. find element starting with "b"
+seek := func(index int, value interface{}) bool {
+    return strings.HasSuffix(value.(string), "b")
+}
+
+// Seek to the condition and continue traversal from that point (in reverse).
+// assumes it.End() was called.
+for found := it.PrevTo(seek); found; found = it.Prev() {
+    index, value := it.Index(), it.Value()
+	...
+}
+```
+
 #### ReverseIteratorWithKey
 
 An [iterator](#iterator) whose elements are referenced by a key. Provides all functions as [IteratorWithKey](#iteratorwithkey), but can also be used for reverse iteration.
@@ -1052,6 +1100,20 @@ if it.Last() {
 }
 ```
 
+```go
+// Seek function, i.e. find element starting with "b"
+seek := func(key interface{}, value interface{}) bool {
+    return strings.HasSuffix(value.(string), "b")
+}
+
+// Seek to the condition and continue traversal from that point (in reverse).
+// assumes it.End() was called.
+for found := it.PrevTo(seek); found; found = it.Prev() {
+    key, value := it.Key(), it.Value()
+	...
+}
+```
+
 ### Enumerable
 
 Enumerable functions for ordered containers that implement [EnumerableWithIndex](#enumerablewithindex) or [EnumerableWithKey](#enumerablewithkey) interfaces.
@@ -1489,13 +1551,19 @@ Coding style:
 
 ```shell
 # Install tooling and set path:
-go get github.com/golang/lint/golint
-go get github.com/fzipp/gocyclo
-go get github.com/kisielk/errcheck
+go install gotest.tools/gotestsum@latest
+go install golang.org/x/lint/golint@latest
+go install github.com/kisielk/errcheck@latest
 export PATH=$PATH:$GOPATH/bin
 
 # Fix errors and warnings:
-go fmt ./... && gofmt -s -w . && go vet ./... && go get ./... && go test ./... && golint ./... && gocyclo -avg -over 15 . && errcheck ./...
+go fmt ./... &&
+go test -v ./... && 
+golint -set_exit_status ./... && 
+! go fmt ./... 2>&1 | read &&
+go vet -v ./... &&
+gocyclo -avg -over 15 ../gods &&
+errcheck ./...
 ```
 
 ### License

containers/iterator.go

@@ -28,6 +28,12 @@ type IteratorWithIndex interface {
 	// If First() returns true, then first element's index and value can be retrieved by Index() and Value().
 	// Modifies the state of the iterator.
 	First() bool
+
+	// NextTo moves the iterator to the next element from current position that satisfies the condition given by the
+	// passed function, and returns true if there was a next element in the container.
+	// If NextTo() returns true, then next element's index and value can be retrieved by Index() and Value().
+	// Modifies the state of the iterator.
+	NextTo(func(index int, value interface{}) bool) bool
 }
 
 // IteratorWithKey is a stateful iterator for ordered containers whose elements are key value pairs.
@@ -54,6 +60,12 @@ type IteratorWithKey interface {
 	// If First() returns true, then first element's key and value can be retrieved by Key() and Value().
 	// Modifies the state of the iterator.
 	First() bool
+
+	// NextTo moves the iterator to the next element from current position that satisfies the condition given by the
+	// passed function, and returns true if there was a next element in the container.
+	// If NextTo() returns true, then next element's key and value can be retrieved by Key() and Value().
+	// Modifies the state of the iterator.
+	NextTo(func(key interface{}, value interface{}) bool) bool
 }
 
 // ReverseIteratorWithIndex is stateful iterator for ordered containers whose values can be fetched by an index.
@@ -80,6 +92,12 @@ type ReverseIteratorWithIndex interface {
 	// Modifies the state of the iterator.
 	Last() bool
 
+	// PrevTo moves the iterator to the previous element from current position that satisfies the condition given by the
+	// passed function, and returns true if there was a next element in the container.
+	// If PrevTo() returns true, then next element's index and value can be retrieved by Index() and Value().
+	// Modifies the state of the iterator.
+	PrevTo(func(index int, value interface{}) bool) bool
+
 	IteratorWithIndex
 }
 
@@ -105,5 +123,11 @@ type ReverseIteratorWithKey interface {
 	// Modifies the state of the iterator.
 	Last() bool
 
+	// PrevTo moves the iterator to the previous element from current position that satisfies the condition given by the
+	// passed function, and returns true if there was a next element in the container.
+	// If PrevTo() returns true, then next element's key and value can be retrieved by Key() and Value().
+	// Modifies the state of the iterator.
+	PrevTo(func(key interface{}, value interface{}) bool) bool
+
 	IteratorWithKey
 }

examples/iteratorwithindex/iteratorwithindex.go

@@ -7,6 +7,7 @@ package main
 import (
 	"fmt"
 	"github.com/emirpasic/gods/sets/treeset"
+	"strings"
 )
 
 // IteratorWithIndexExample to demonstrate basic usage of IteratorWithIndex
@@ -48,4 +49,32 @@ func main() {
 		fmt.Print("\nLast index: ", it.Index()) // Last index: 3
 		fmt.Print("\nLast value: ", it.Value()) // Last value: c
 	}
+
+	// Seek element starting with "b"
+	seek := func(index int, value interface{}) bool {
+		return strings.HasSuffix(value.(string), "b")
+	}
+
+	it.Begin()
+	for found := it.NextTo(seek); found; found = it.Next() {
+		fmt.Print("\nNextTo index: ", it.Index())
+		fmt.Print("\nNextTo value: ", it.Value())
+	} /*
+		NextTo index: 1
+		NextTo value: "b"
+		NextTo index: 2
+		NextTo value: "c"
+	*/
+
+	it.End()
+	for found := it.PrevTo(seek); found; found = it.Prev() {
+		fmt.Print("\nNextTo index: ", it.Index())
+		fmt.Print("\nNextTo value: ", it.Value())
+	} /*
+		NextTo index: 1
+		NextTo value: "b"
+		NextTo index: 0
+		NextTo value: "a"
+	*/
+
 }

examples/iteratorwithkey/iteratorwithkey.go

@@ -7,14 +7,15 @@ package main
 import (
 	"fmt"
 	"github.com/emirpasic/gods/maps/treemap"
+	"strings"
 )
 
 // IteratorWithKeyExample to demonstrate basic usage of IteratorWithKey
 func main() {
 	m := treemap.NewWithIntComparator()
-	m.Put(1, "a")
-	m.Put(2, "b")
-	m.Put(3, "a")
+	m.Put(0, "a")
+	m.Put(1, "b")
+	m.Put(2, "c")
 	it := m.Iterator()
 
 	fmt.Print("\nForward iteration\n")
@@ -47,7 +48,34 @@ func main() {
 	}
 
 	if it.Last() {
-		fmt.Print("\nLast key: ", it.Key())     // Last key: 3
+		fmt.Print("\nLast key: ", it.Key())     // Last key: 2
 		fmt.Print("\nLast value: ", it.Value()) // Last value: c
 	}
+
+	// Seek key-value pair whose value starts with "b"
+	seek := func(key interface{}, value interface{}) bool {
+		return strings.HasSuffix(value.(string), "b")
+	}
+
+	it.Begin()
+	for found := it.NextTo(seek); found; found = it.Next() {
+		fmt.Print("\nNextTo key: ", it.Key())
+		fmt.Print("\nNextTo value: ", it.Value())
+	} /*
+		NextTo key: 1
+		NextTo value: "b"
+		NextTo key: 2
+		NextTo value: "c"
+	*/
+
+	it.End()
+	for found := it.PrevTo(seek); found; found = it.Prev() {
+		fmt.Print("\nNextTo key: ", it.Key())
+		fmt.Print("\nNextTo value: ", it.Value())
+	} /*
+		NextTo key: 1
+		NextTo value: "b"
+		NextTo key: 0
+		NextTo value: "a"
+	*/
 }

lists/arraylist/arraylist_test.go

@@ -7,6 +7,7 @@ package arraylist
 import (
 	"fmt"
 	"github.com/emirpasic/gods/utils"
+	"strings"
 	"testing"
 )
 
@@ -500,6 +501,106 @@ func TestListIteratorLast(t *testing.T) {
 	}
 }
 
+func TestListIteratorNextTo(t *testing.T) {
+	// Sample seek function, i.e. string starting with "b"
+	seek := func(index int, value interface{}) bool {
+		return strings.HasSuffix(value.(string), "b")
+	}
+
+	// NextTo (empty)
+	{
+		list := New()
+		it := list.Iterator()
+		for it.NextTo(seek) {
+			t.Errorf("Shouldn't iterate on empty list")
+		}
+	}
+
+	// NextTo (not found)
+	{
+		list := New()
+		list.Add("xx", "yy")
+		it := list.Iterator()
+		for it.NextTo(seek) {
+			t.Errorf("Shouldn't iterate on empty list")
+		}
+	}
+
+	// NextTo (found)
+	{
+		list := New()
+		list.Add("aa", "bb", "cc")
+		it := list.Iterator()
+		it.Begin()
+		if !it.NextTo(seek) {
+			t.Errorf("Shouldn't iterate on empty list")
+		}
+		if index, value := it.Index(), it.Value(); index != 1 || value.(string) != "bb" {
+			t.Errorf("Got %v,%v expected %v,%v", index, value, 1, "bb")
+		}
+		if !it.Next() {
+			t.Errorf("Should go to first element")
+		}
+		if index, value := it.Index(), it.Value(); index != 2 || value.(string) != "cc" {
+			t.Errorf("Got %v,%v expected %v,%v", index, value, 2, "cc")
+		}
+		if it.Next() {
+			t.Errorf("Should not go past last element")
+		}
+	}
+}
+
+func TestListIteratorPrevTo(t *testing.T) {
+	// Sample seek function, i.e. string starting with "b"
+	seek := func(index int, value interface{}) bool {
+		return strings.HasSuffix(value.(string), "b")
+	}
+
+	// PrevTo (empty)
+	{
+		list := New()
+		it := list.Iterator()
+		it.End()
+		for it.PrevTo(seek) {
+			t.Errorf("Shouldn't iterate on empty list")
+		}
+	}
+
+	// PrevTo (not found)
+	{
+		list := New()
+		list.Add("xx", "yy")
+		it := list.Iterator()
+		it.End()
+		for it.PrevTo(seek) {
+			t.Errorf("Shouldn't iterate on empty list")
+		}
+	}
+
+	// PrevTo (found)
+	{
+		list := New()
+		list.Add("aa", "bb", "cc")
+		it := list.Iterator()
+		it.End()
+		if !it.PrevTo(seek) {
+			t.Errorf("Shouldn't iterate on empty list")
+		}
+		if index, value := it.Index(), it.Value(); index != 1 || value.(string) != "bb" {
+			t.Errorf("Got %v,%v expected %v,%v", index, value, 1, "bb")
+		}
+		if !it.Prev() {
+			t.Errorf("Should go to first element")
+		}
+		if index, value := it.Index(), it.Value(); index != 0 || value.(string) != "aa" {
+			t.Errorf("Got %v,%v expected %v,%v", index, value, 0, "aa")
+		}
+		if it.Prev() {
+			t.Errorf("Should not go before first element")
+		}
+	}
+}
+
 func TestListSerialization(t *testing.T) {
 	list := New()
 	list.Add("a", "b", "c")