Slice: Add count func (#15)

Returns the count of matched elements

README.md

@@ -420,6 +420,7 @@ func Union(slices ...interface{}) interface{} //Union creates a slice of unique
 func UpdateByIndex(slice interface{}, index int, value interface{}) (interface{}, error) //update the slice element at index.
 func Without(slice interface{}, values ...interface{}) interface{} //creates a slice excluding all given values
 func GroupBy(slice, function interface{}) (interface{}, interface{}) // groups slice into two categories
+func Count(slice, function interface{}) int // Count iterates over elements of slice, returns a count of all matched elements
 ```
 
 #### 10. strutil is for processing string

README_zh-CN.md

@@ -421,6 +421,7 @@ func Union(slices ...interface{}) interface{} //slice并集, 去重
 func UpdateByIndex(slice interface{}, index int, value interface{}) (interface{}, error) //在切片中index位置更新value
 func Without(slice interface{}, values ...interface{}) interface{} //slice去除values
 func GroupBy(slice, function interface{}) (interface{}, interface{}) //根据函数function的逻辑分slice为两组slice
+func Count(slice, function interface{}) int 
 ```
 
 #### 10. strutil字符串处理包

slice/slice.go

@@ -187,6 +187,28 @@ func Filter(slice, function interface{}) interface{} {
 	return res.Interface()
 }
 
+// Count iterates over elements of slice, returns a count of all matched elements
+// The function signature should be func(index int, value interface{}) bool .
+func Count(slice, function interface{}) int {
+	sv := sliceValue(slice)
+	fn := functionValue(function)
+
+	elemType := sv.Type().Elem()
+	if checkSliceCallbackFuncSignature(fn, elemType, reflect.ValueOf(true).Type()) {
+		panic("function param should be of type func(int, " + elemType.String() + ")" + reflect.ValueOf(true).Type().String())
+	}
+
+	var counter int
+	for i := 0; i < sv.Len(); i++ {
+		flag := fn.Call([]reflect.Value{reflect.ValueOf(i), sv.Index(i)})[0]
+		if flag.Bool() {
+			counter++
+		}
+	}
+
+	return counter
+}
+
 // GroupBy iterate over elements of the slice, each element will be group by criteria, returns two slices
 // The function signature should be func(index int, value interface{}) bool .
 func GroupBy(slice, function interface{}) (interface{}, interface{}) {

slice/slice_test.go

@@ -197,6 +197,19 @@ func TestGroupBy(t *testing.T) {
 	}
 }
 
+func TestCount(t *testing.T) {
+	nums := []int{1, 2, 3, 4, 5, 6}
+	evenFunc := func(i, num int) bool {
+		return (num % 2) == 0
+	}
+	c := Count(nums, evenFunc)
+
+	if c != 3 {
+		internal.LogFailedTestInfo(t, "Count", nums, 3, c)
+		t.FailNow()
+	}
+}
+
 func TestFind(t *testing.T) {
 	nums := []int{1, 2, 3, 4, 5}
 	even := func(i, num int) bool {