fix: Avoid redundant deep cloning when unwinding. (#286)

* Avoid redundant deep cloning when unwinding.

* Attempt to improve readability of unwindData(...)

* Improve formatting.

lib/JSON2CSVBase.js

@@ -78,7 +78,7 @@ class JSON2CSVBase {
    */
   processRow(row) {
     if (!row
-        || (Object.getOwnPropertyNames(row).length === 0 
+        || (Object.getOwnPropertyNames(row).length === 0
           && !this.opts.includeEmptyRows)) {
       return undefined;
     }
@@ -114,7 +114,7 @@ class JSON2CSVBase {
     const defaultValue = typeof fieldInfo === 'object' && 'default' in fieldInfo
       ? fieldInfo.default
       : this.opts.defaultValue;
-    
+
     let value;
     if (fieldInfo) {
       if (typeof fieldInfo === 'string') {
@@ -231,42 +231,45 @@ class JSON2CSVBase {
    * @param {Object} dataRow Original JSON object
    * @param {String[]} unwindPaths The paths as strings to be used to deconstruct the array
    * @returns {Array} Array of objects containing all rows after unwind of chosen paths
-   */
+  */
   unwindData(dataRow, unwindPaths) {
-    return unwindPaths
-      .reduce((data, unwindPath) =>
-        data.map((dataEl) => {
-          const unwindArray = lodashGet(dataEl, unwindPath);
+    const unwind = (rows, unwindPath) => {
+      function clone(o) {
+        return unwindPath.indexOf('.') !== -1
+          ? lodashCloneDeep(o)
+          : Object.assign({}, o);
+      }
+
+      return rows
+        .map(row => {
+          const unwindArray = lodashGet(row, unwindPath);
 
           if (!Array.isArray(unwindArray)) {
-            return dataEl;
+            return row;
           }
 
-          if (unwindArray.length) {
-            return unwindArray.map((unwindEl, index) => {
-              const dataCopy = lodashCloneDeep(dataEl);
+          if (!unwindArray.length) {
+            return lodashSet(clone(row), unwindPath, undefined);
+          }
 
-              if (this.opts.unwindBlank && index > 0) {
-                Object.keys(dataCopy).forEach(key => {
-                  if (!unwindEl[key]) {
-                    dataCopy[key] = null;
-                  }
-                })
-              }
+          return unwindArray.map((unwindRow, index) => {
+            const clonedRow = clone(row);
+            const shouldBlank = this.opts.unwindBlank && index > 0;
 
+            if (shouldBlank) {
+              const parentKeys = Object.keys(clonedRow).filter(
+                key => !unwindRow[key]
+              );
+              parentKeys.forEach(key => (clonedRow[key] = null));
+            }
 
-              lodashSet(dataCopy, unwindPath, unwindEl);
-              return dataCopy;
-            });
-          }
+            return lodashSet(clonedRow, unwindPath, unwindRow);
+          });
+        })
+        .reduce((a, e) => a.concat(e), []);
+    };
 
-          const dataCopy = lodashCloneDeep(dataEl);
-          lodashSet(dataCopy, unwindPath, undefined);
-          return dataCopy;
-        }).reduce((tempData, rows) => tempData.concat(rows), []),
-      [dataRow]
-    )
-    .reduce((tempData, rows) => tempData.concat(rows), []);
+    return unwindPaths.reduce(unwind, [dataRow]);
   }
 }