diff --git a/src/implements/methods.ts b/src/implements/methods.ts
index 43d764e..52e6b23 100644
--- a/src/implements/methods.ts
+++ b/src/implements/methods.ts
@@ -1,14 +1,12 @@
 import { IMethods, IIterator } from "../intefaces";
-import { Utils } from '../utils/object';
+import { Utils } from '../utils';
 import {
     WhereClause, SelectClause, SelectManyClause, JoinClause, LeftJoinClause, OrderByClause,
     OrderByDescendingClause, GroupByClause, GroupJoinClause, FirstClause, LastClause, CountClause,
     SumClause, AvarageClause, MinClause, MaxClause, SingleClause, TakeClause, SkipWhileClause,
-    SkipClause, TakeWhileClause, AnyClause, ContainsClause, AllClause
+    SkipClause, TakeWhileClause, AnyClause, ContainsClause, AllClause, DistinctClause, ConcatClause
 } from "../methods";
 import { Queryable } from './queryable';
-import { DistinctClause } from '../methods/distinct';
-import { ConcatClause } from '../methods/concat';
 
 export class IteratorMethods<T> implements IMethods<T> {
 
diff --git a/src/methods/all.ts b/src/methods/all.ts
index b4a6a63..f852e18 100644
--- a/src/methods/all.ts
+++ b/src/methods/all.ts
@@ -5,7 +5,7 @@ export class AllClause<T> extends BaseIterator<T> implements IIterator<T> {
 
     _iterator: (item: T) => boolean;
 
-    execute(source: T[] | any[]): T[] | T | any {
+    execute(source: T[]): boolean {
         if (!source) return false;
         else {
             return (source as T[]).every((x) => {
diff --git a/src/methods/any.ts b/src/methods/any.ts
index 037e8af..02eb55c 100644
--- a/src/methods/any.ts
+++ b/src/methods/any.ts
@@ -5,7 +5,7 @@ export class AnyClause<T> extends BaseIterator<T> implements IIterator<T> {
 
     _iterator: (item: T) => boolean;
 
-    execute(source: T[] | any[]): T[] | T | any {
+    execute(source: T[]): boolean {
         if (!source) return false;
         else {
             return (source as T[]).some((x) => {
diff --git a/src/methods/average.ts b/src/methods/average.ts
index 6b41707..8516d05 100644
--- a/src/methods/average.ts
+++ b/src/methods/average.ts
@@ -6,12 +6,12 @@ export class AvarageClause<T> extends BaseIterator<T> implements IIterator<T> {
 
     _iterator: (item: T) => any;
 
-    execute(source: any[] | T[]): T[] | T | any {
+    execute(source: T[]): number {
         if (!source) return 0;
 
-        let _result = this._iterator
+        let _result = (this._iterator
             ? new SelectClause(this._iterator).execute(source) as number[]
-            : source;
+            : source) as number[];
 
         if (!_result) return 0;
         if (Number.isNaN(_result[0])) throw new Error("Avarage operator need type of number");
diff --git a/src/methods/contains.ts b/src/methods/contains.ts
index d6fc5c8..59ff691 100644
--- a/src/methods/contains.ts
+++ b/src/methods/contains.ts
@@ -1,5 +1,6 @@
 import { IIterator } from "../intefaces/iterator.interface";
 import { BaseIterator } from "../implements/baseIterator";
+import { Utils } from '../utils';
 
 export class ContainsClause<T> extends BaseIterator<T> implements IIterator<T> {
 
@@ -11,7 +12,7 @@ export class ContainsClause<T> extends BaseIterator<T> implements IIterator<T> {
 
         let _flag = false;
         for (let i = 0, li = source.length; i < li; i++) {
-            if (source[i] === this._entity) {
+            if (Utils.compare(source[i], this._entity)) {
                 _flag = true;
                 break;
             }
diff --git a/src/methods/count.ts b/src/methods/count.ts
index afe317e..715439b 100644
--- a/src/methods/count.ts
+++ b/src/methods/count.ts
@@ -5,13 +5,13 @@ export class CountClause<T> extends BaseIterator<T> implements IIterator<T> {
 
     _iterator: (item: T) => boolean;
 
-    execute(source: any[] | T[]): T[] | T | any {
-        if (!source) return source.length;
+    execute(source: T[]): number {
+        if (!source) return 0;
         else if (!this._iterator) return source.length;
         else {
             return (source as T[]).filter((x) => {
                 return this._iterator(x);
-            }).length;
+            }).length || 0;
         }
     }
 
diff --git a/src/methods/first.ts b/src/methods/first.ts
index 5762b4a..a75cc22 100644
--- a/src/methods/first.ts
+++ b/src/methods/first.ts
@@ -5,10 +5,9 @@ export class FirstClause<T> extends BaseIterator<T> implements IIterator<T> {
 
     _iterator: (item: T) => boolean;
 
-    execute(source: any[] | T[]): T[] | T {
-        if (!this._iterator) {
+    execute(source: T[]): T {
+        if (!this._iterator)
             return source[0];
-        }
         else {
             return (source as T[]).filter((x) => {
                 return this._iterator(x);
diff --git a/src/methods/groupBy.ts b/src/methods/groupBy.ts
index 6bd47a1..e3c9d71 100644
--- a/src/methods/groupBy.ts
+++ b/src/methods/groupBy.ts
@@ -1,6 +1,7 @@
 import { IIterator } from "../intefaces/iterator.interface";
 import { SelectClause } from "./select";
 import { BaseIterator } from "../implements/baseIterator";
+import { Utils } from '../utils';
 
 export class GroupByClause<T> extends BaseIterator<T> implements IIterator<T> {
 
@@ -13,7 +14,7 @@ export class GroupByClause<T> extends BaseIterator<T> implements IIterator<T> {
         let _mappingSource = {}; // Object contains all data in array follow by [index] : {object}
         let _indexes = [] as Array<{ value, index }>; // Make indexes table base on iterator function
         let _groupByObj = {} // Object contains [groupByValue] : <any>[]
-        let _distinctGroupByValues = this.distinct
+        let _distinctGroupByValues = Utils.distinct
             (new SelectClause(this._iterator).execute(source));
 
         // Make mapping source by indexes
@@ -52,10 +53,4 @@ export class GroupByClause<T> extends BaseIterator<T> implements IIterator<T> {
         super();
         this._iterator = func;
     }
-
-    private distinct(array: any[]) {
-        return array.filter((val, index, self) => {
-            return self.indexOf(val) === index;
-        }).filter(x => x != undefined);
-    }
 }
\ No newline at end of file
diff --git a/src/methods/groupJoin.ts b/src/methods/groupJoin.ts
index 1320c99..a455eb4 100644
--- a/src/methods/groupJoin.ts
+++ b/src/methods/groupJoin.ts
@@ -6,7 +6,7 @@ import { BaseIterator } from "../implements/baseIterator";
 
 export class GroupJoinClause<T, S> extends BaseIterator<T> implements IIterator<T> {
 
-    nextSource: any[] | Promise<any[]>;
+    nextSource: any[];
 
     _joinIterator: (aEntity: T, bEntity: S) => boolean;
 
@@ -35,10 +35,4 @@ export class GroupJoinClause<T, S> extends BaseIterator<T> implements IIterator<
         this._groupIterator = groupIterator;
         this.nextSource = anotherSource;
     }
-
-    private distinct(array: any[]) {
-        return array.filter((val, index, self) => {
-            return self.indexOf(val) === index;
-        }).filter(x => x != undefined);
-    }
 }
\ No newline at end of file
diff --git a/src/methods/index.ts b/src/methods/index.ts
index 95a6865..c6162f5 100644
--- a/src/methods/index.ts
+++ b/src/methods/index.ts
@@ -21,4 +21,6 @@ export * from './sum';
 export * from './take';
 export * from './takeWhile';
 export * from './where';
-export * from './all';
\ No newline at end of file
+export * from './all';
+export * from './concat';
+export * from './distinct';
\ No newline at end of file
diff --git a/src/methods/join.ts b/src/methods/join.ts
index 6bfea68..4d75b4c 100644
--- a/src/methods/join.ts
+++ b/src/methods/join.ts
@@ -7,7 +7,7 @@ export class JoinClause<T, S> extends BaseIterator<T> implements IIterator<T> {
 
     nextSource: S[] | Promise<S[]>;
 
-    execute(source: any[] | T[]): T[] | any[] {
+    execute(source: T[]): { x: T, y: S }[] {
         if (source) {
             let _result = [];
             for (let i = 0, li = source.length; i < li; i++) {
@@ -24,7 +24,7 @@ export class JoinClause<T, S> extends BaseIterator<T> implements IIterator<T> {
             }
             return _result;
         }
-        return source;
+        return source as any;
     }
 
     constructor(anotherSource: S[] | Promise<S[]>, func: (item1: T, item2: S) => boolean) {
diff --git a/src/methods/last.ts b/src/methods/last.ts
index f16a00e..b944daf 100644
--- a/src/methods/last.ts
+++ b/src/methods/last.ts
@@ -5,10 +5,8 @@ export class LastClause<T> extends BaseIterator<T> implements IIterator<T> {
 
     _iterator: (item: T) => boolean;
 
-    execute(source: any[] | T[]): T[] | T {
-        if (!source) {
-            return source[source.length];
-        }
+    execute(source: T[]): T {
+        if (!source) return null;
         else {
             if (!this._iterator) return source[source.length - 1];
             return (source as T[]).filter((x) => {
diff --git a/src/methods/leftJoin.ts b/src/methods/leftJoin.ts
index f9d0f1b..17b8d3d 100644
--- a/src/methods/leftJoin.ts
+++ b/src/methods/leftJoin.ts
@@ -5,9 +5,9 @@ export class LeftJoinClause<T, S> extends BaseIterator<T> implements IIterator<T
 
     _iterator: (item1: T, item2: S) => boolean;
 
-    nextSource: any[] | Promise<any[]>;
+    nextSource: S[] | Promise<S[]>;
 
-    execute(source: any[] | T[]): T[] | any[] {
+    execute(source: T[]): any[] {
         if (source) {
             let _result = [];
             for (let i = 0, li = source.length; i < li; i++) {
diff --git a/src/methods/max.ts b/src/methods/max.ts
index 3cff5e5..f2d70ba 100644
--- a/src/methods/max.ts
+++ b/src/methods/max.ts
@@ -6,14 +6,17 @@ export class MaxClause<T> extends BaseIterator<T> implements IIterator<T> {
 
     _iterator: (item: T) => any;
 
-    execute(source: any[] | T[]): T[] | T | any {
+    execute(source: T[]): number {
         if (!source) return 0;
 
-        let _result = new SelectClause(this._iterator).execute(source) as number[];
+        let _result;
+
+        if (this._iterator)
+            _result = new SelectClause(this._iterator).execute(source) as number[];
 
         if (!_result) return 0;
 
-        if (!Number.isNaN(_result[0])) throw new Error("Sum operator require type of number");
+        if (!Number.isNaN(_result[0])) throw new Error("Max operator require type of number");
 
         return Math.max(..._result);
     }
diff --git a/src/methods/min.ts b/src/methods/min.ts
index 3b52c83..2976f1e 100644
--- a/src/methods/min.ts
+++ b/src/methods/min.ts
@@ -6,14 +6,17 @@ export class MinClause<T> extends BaseIterator<T> implements IIterator<T> {
 
     _iterator: (item: T) => any;
 
-    execute(source: any[] | T[]): T[] | T | any {
+    execute(source: T[]): number {
         if (!source) return 0;
 
-        let _result = new SelectClause(this._iterator).execute(source) as number[];
+        let _result;
+        
+        if(this._iterator)
+            _result = new SelectClause(this._iterator).execute(source) as number[];
 
         if (!_result) return 0;
 
-        if (!Number.isNaN(_result[0])) throw new Error("Sum operator require type of number");
+        if (!Number.isNaN(_result[0])) throw new Error("Min operator require type of number");
 
         return Math.min(..._result);
     }
diff --git a/src/methods/orderBy.ts b/src/methods/orderBy.ts
index b4f736c..32ce19e 100644
--- a/src/methods/orderBy.ts
+++ b/src/methods/orderBy.ts
@@ -6,7 +6,7 @@ export class OrderByClause<T> extends BaseIterator<T> implements IIterator<T> {
 
     _iterator: (item: T) => any;
 
-    execute(source: T[]): T[] | any[] {
+    execute(source: T[]): T[] {
 
         if (!source) return null;
 
diff --git a/src/methods/orderByDescending.ts b/src/methods/orderByDescending.ts
index 54b4e03..0357878 100644
--- a/src/methods/orderByDescending.ts
+++ b/src/methods/orderByDescending.ts
@@ -6,7 +6,7 @@ export class OrderByDescendingClause<T> extends BaseIterator<T> implements IIter
 
     _iterator: (item: T) => any;
 
-    execute(source: T[]): T[] | any[] {
+    execute(source: T[]): T[] {
 
         if (!source) return null;
 
diff --git a/src/methods/select.ts b/src/methods/select.ts
index 37fdd98..f72ca88 100644
--- a/src/methods/select.ts
+++ b/src/methods/select.ts
@@ -5,7 +5,7 @@ export class SelectClause<T> extends BaseIterator<T> implements IIterator<T> {
 
     _iterator: (item: T) => boolean;
 
-    execute(source: any[] | T[]): T[] | any[] {
+    execute(source: T[]): any[]{
         if (source) {
             return (source as T[]).map(x => (this._iterator(x)));
         }
diff --git a/src/methods/selectMany.ts b/src/methods/selectMany.ts
index 1a52be9..defaa05 100644
--- a/src/methods/selectMany.ts
+++ b/src/methods/selectMany.ts
@@ -6,7 +6,7 @@ export class SelectManyClause<T> extends BaseIterator<T> implements IIterator<T>
 
     _iterator: (item: T, index?: number) => any;
 
-    execute(source: any[] | T[]): T[] | any[] {
+    execute(source: T[]): any[] {
         if (!source) return null;
 
         let _result = new SelectClause(this._iterator).execute(source);
diff --git a/src/methods/single.ts b/src/methods/single.ts
index eb75a96..6041446 100644
--- a/src/methods/single.ts
+++ b/src/methods/single.ts
@@ -1,25 +1,20 @@
 import { IIterator } from "../intefaces/iterator.interface";
 import { WhereClause } from "./where";
 import { BaseIterator } from "../implements/baseIterator";
+import { Utils } from '../utils';
 
 export class SingleClause<T> extends BaseIterator<T> implements IIterator<T> {
 
     _iterator: (item: T) => boolean;
 
-    execute(source: any[] | T[]): T {
-        if (!this._iterator) {
-            return this.getSingle(source);
-        }
-        else {
-            let _result = new WhereClause(this._iterator).execute(source);
-            return this.getSingle(_result);
-        }
-    }
+    execute(source: T[]): T {
+
+        let _result = source;
+
+        if (this._iterator)
+            _result = new WhereClause(this._iterator).execute(_result);
 
-    private getSingle(src: any[] | T[]): T | any {
-        if (src.length > 1) throw new Error("The collection does not contain exactly one element");
-        else if (src.length === 1)
-            return src[0];
+        return Utils.getSingle(_result);
     }
 
     constructor(func?: (item: T) => boolean) {
diff --git a/src/methods/skip.ts b/src/methods/skip.ts
index 0262ac0..2c36411 100644
--- a/src/methods/skip.ts
+++ b/src/methods/skip.ts
@@ -5,9 +5,9 @@ export class SkipClause<T> extends BaseIterator<T> implements IIterator<T> {
 
     _iterator: number;
 
-    execute(source: any[] | T[]): T[] | any[] {
+    execute(source: T[]): T[]{
         if (source) {
-            return (source as T[]).slice(this._iterator);
+            return source.slice(this._iterator);
         }
         return source;
     }
diff --git a/src/methods/skipWhile.ts b/src/methods/skipWhile.ts
index e38f733..827b5d5 100644
--- a/src/methods/skipWhile.ts
+++ b/src/methods/skipWhile.ts
@@ -6,15 +6,15 @@ export class SkipWhileClause<T> extends BaseIterator<T> implements IIterator<T>
 
     _iterator: (item: T) => boolean;
 
-    execute(source: any[] | T[]): T[] | any[] {
+    execute(source: T[]): T[]{
         if (source) {
             let _skipCount = 0;
-            for (let i = 0; i < (source as T[]).length; i++) {
+            for (let i = 0; i < source.length; i++) {
                 const _item = source[i];
                 if (this._iterator(_item)) break;
                 _skipCount += 1;
             }
-            return new SkipClause(_skipCount).execute(source);
+            return new SkipClause<T>(_skipCount).execute(source);
         }
         return null;
     }
diff --git a/src/methods/sum.ts b/src/methods/sum.ts
index dca6131..7b850c0 100644
--- a/src/methods/sum.ts
+++ b/src/methods/sum.ts
@@ -6,10 +6,13 @@ export class SumClause<T> extends BaseIterator<T> implements IIterator<T> {
 
     _iterator: (item: T) => any;
 
-    execute(source: any[] | T[]): T[] | T | any {
+    execute(source: T[]): number {
         if (!source) return 0;
 
-        let _result = new SelectClause(this._iterator).execute(source) as number[];
+        let _result;
+
+        if (this._iterator)
+            _result = new SelectClause(this._iterator).execute(source) as number[];
 
         if (!_result) return 0;
 
diff --git a/src/methods/take.ts b/src/methods/take.ts
index 6fd20cf..3113b49 100644
--- a/src/methods/take.ts
+++ b/src/methods/take.ts
@@ -5,7 +5,7 @@ export class TakeClause<T> extends BaseIterator<T> implements IIterator<T> {
 
     _iterator: number;
 
-    execute(source: any[] | T[]): T[] | any[] {
+    execute(source: T[]): T[]{
         if (source) {
             return (source as T[]).slice(0, this._iterator);
         }
diff --git a/src/methods/takeWhile.ts b/src/methods/takeWhile.ts
index 9b444f4..b9de863 100644
--- a/src/methods/takeWhile.ts
+++ b/src/methods/takeWhile.ts
@@ -6,7 +6,7 @@ export class TakeWhileClause<T> extends BaseIterator<T> implements IIterator<T>
 
     _iterator: (item: T) => boolean;
 
-    execute(source: any[] | T[]): T[] | any[] {
+    execute(source: T[]): T[]{
         if (source) {
             let _takeCount = 0;
             for (let i = 0; i < (source as T[]).length; i++) {
@@ -14,7 +14,7 @@ export class TakeWhileClause<T> extends BaseIterator<T> implements IIterator<T>
                 if (this._iterator(_item)) break;
                 _takeCount += 1;
             }
-            return new TakeClause(_takeCount).execute(source);
+            return new TakeClause<T>(_takeCount).execute(source);
         }
         return null;
     }
diff --git a/src/methods/where.ts b/src/methods/where.ts
index 83317c2..ad18e01 100644
--- a/src/methods/where.ts
+++ b/src/methods/where.ts
@@ -5,7 +5,7 @@ export class WhereClause<T> extends BaseIterator<T> implements IIterator<T> {
 
     _iterator: (item: T) => boolean;
 
-    execute(source: any[] | T[]): T[] | any[] {
+    execute(source: T[]): T[]{
         if (source) {
             return (source as T[]).filter((x) => {
                 return this._iterator(x);
diff --git a/src/utils/index.ts b/src/utils/index.ts
index 78e028b..5652708 100644
--- a/src/utils/index.ts
+++ b/src/utils/index.ts
@@ -1 +1 @@
-export * from './object';
\ No newline at end of file
+export * from './utility';
\ No newline at end of file
diff --git a/src/utils/object.ts b/src/utils/object.ts
deleted file mode 100644
index 358353d..0000000
--- a/src/utils/object.ts
+++ /dev/null
@@ -1,11 +0,0 @@
-export class Utils {
-    public static isPromise(obj) {
-        return !!obj && (typeof obj === 'object' || typeof obj === 'function') && typeof obj.then === 'function';
-    }
-    
-    public static distinct(array: any[]) {
-        return array.filter((val, index, self) => {
-            return self.indexOf(val) === index;
-        }).filter(x => x != undefined);
-    }
-}
\ No newline at end of file
diff --git a/src/utils/utility.ts b/src/utils/utility.ts
new file mode 100644
index 0000000..9ee9ef4
--- /dev/null
+++ b/src/utils/utility.ts
@@ -0,0 +1,53 @@
+export class Utils {
+    public static isPromise(obj): boolean {
+        return !!obj && (typeof obj === 'object' || typeof obj === 'function') && typeof obj.then === 'function';
+    }
+
+    public static distinct(array: any[]): any[] {
+        return array.filter((val, index, self) => {
+            return self.indexOf(val) === index;
+        }).filter(x => x != undefined);
+    }
+
+    public static getSingle(src: any[]): any {
+        if (src.length > 1) throw new Error("The collection does not contain exactly one element");
+        else if (src.length === 1)
+            return src[0];
+    }
+
+    public static compare(obj: any, obj2: any): boolean {
+        if (obj === obj2) return true;
+
+        const objIsArray = Array.isArray(obj);
+        const obj2IsArray = Array.isArray(obj2);
+
+        if (objIsArray && obj2IsArray) {
+
+            if ((obj as any[]).length !== (obj2 as any[]).length) return false;
+
+            for (let i = 0, li = obj.length; i < li; i++) {
+                const result = this.compare(obj[i], obj2[i]);
+                if (!result) return false;
+            }
+
+            return true;
+
+        } else {
+            const objIsObject = typeof obj === 'object';
+            const obj2IsObject = typeof obj2 === 'object';
+
+            if (objIsObject && obj2IsObject) {
+                const props = Object.keys(objIsObject);
+
+                for (let i = 0, li = props.length; i < li; i++) {
+                    const result = this.compare(objIsObject[props[i]], obj2IsObject[props[i]]);
+                    if (!result) return false;
+                }
+
+                return true;
+            }
+
+            return false;
+        }
+    }
+}
\ No newline at end of file
diff --git a/tsconfig.json b/tsconfig.json
index 93ca402..89c1bee 100644
--- a/tsconfig.json
+++ b/tsconfig.json
@@ -23,7 +23,7 @@
             ]
         },
         "baseUrl": "./",
-        "declaration": true,
+        // "declaration": true,
     },
     "exclude": [
         "demo",