Add Head and Tail operations

src/core/operations/StrUtils.js

@@ -537,6 +537,61 @@ const StrUtils = {
         return output;
     },
 
+    /**
+     * Head lines operation.
+     *
+     * @param {string} input
+     * @param {Object[]} args
+     * @returns {string}
+     */
+    runHead: function(input, args) {
+        let delimiter = args[0],
+            number = args[1],
+            allBut = args[2];
+
+        delimiter = Utils.charRep[delimiter];
+        let splitInput = input.split(delimiter);
+
+        return splitInput
+        .filter((line, lineIndex) => {
+            lineIndex += 1;
+
+            if (allBut) {
+                return lineIndex <= splitInput.length - number;
+            } else {
+                return lineIndex <= number;
+            }
+        })
+        .join(delimiter);
+    },
+
+    /**
+     * Tail lines operation.
+     *
+     * @param {string} input
+     * @param {Object[]} args
+     * @returns {string}
+     */
+    runTail: function(input, args) {
+        let delimiter = args[0],
+            number = args[1],
+            allBut = args[2];
+
+        delimiter = Utils.charRep[delimiter];
+        let splitInput = input.split(delimiter);
+
+        return splitInput
+        .filter((line, lineIndex) => {
+            lineIndex += 1;
+
+            if (allBut) {
+                return lineIndex >= number;
+            } else {
+                return lineIndex > splitInput.length - number;
+            }
+        })
+        .join(delimiter);
+    },
 };
 
 export default StrUtils;