Added method filter in methodchain

Author: Sah, Nandeshwar

.circleci/config.yml

@@ -3,7 +3,7 @@ jobs: # basic units of work in a run
   build: # runs not using Workflows must have a `build` job as entry point
     docker: # run the steps with Docker
       # CircleCI Go images available at: https://hub.docker.com/r/circleci/golang/
-      - image: circleci/golang:1.11 #
+      - image: circleci/golang:1.15 #
 
     # directory where steps are run. Path must conform to the Go Workspace requirements
     working_directory: /go/src/github.com/logic-building/functional-go/

fp/filter.go

@@ -376,3 +376,22 @@ func FilterStr(f func(string) bool, list []string) []string {
 	}
 	return newList
 }
+
+// FilterBool takes two arguments
+//  1. Function: takes 1 argument of type bool and returns bool
+//  2. slice of type []bool
+//
+// Returns:
+//  new filtered list
+func FilterBool(f func(bool) bool, list []bool) []bool {
+	if f == nil {
+		return []bool{}
+	}
+	var newList []bool
+	for _, v := range list {
+		if f(v) {
+			newList = append(newList, v)
+		}
+	}
+	return newList
+}

fp/filter_test.go

@@ -365,3 +365,22 @@ func TestFilterStr(t *testing.T) {
 func isStringLengthLessThan10(str string) bool {
 	return len(str) < 10
 }
+
+func TestFilterBool(t *testing.T) {
+	var vt bool = true
+
+	expectedSumList := []bool{vt}
+
+	newList := FilterBool(trueBool, []bool{vt})
+	if newList[0] != expectedSumList[0] {
+		t.Errorf("FilterBoolPtr failed")
+	}
+
+	if len(FilterBoolPtr(nil, nil)) > 0 {
+		t.Errorf("MapBoolPtr failed.")
+	}
+}
+
+func trueBool(num1 bool) bool {
+	return true
+}

fp/map.go

@@ -346,3 +346,23 @@ func MapStr(f func(string) string, list []string) []string {
 	}
 	return newList
 }
+
+// MapBool applies the function(1st argument) on each item of the list and returns new list
+//
+// Takes 2 inputs
+//	1. Function - takes 1 input
+//	2. List
+//
+// Returns
+//	New List.
+//	Empty list if all arguments are nil or either one is nil
+func MapBool(f func(bool) bool, list []bool) []bool {
+	if f == nil {
+		return []bool{}
+	}
+	newList := make([]bool, len(list))
+	for i, v := range list {
+		newList[i] = f(v)
+	}
+	return newList
+}