diff --git a/danfojs-browser/src/core/frame.js b/danfojs-browser/src/core/frame.js
index 7e38aff9..af460e9b 100644
--- a/danfojs-browser/src/core/frame.js
+++ b/danfojs-browser/src/core/frame.js
@@ -1237,7 +1237,7 @@ export default class DataFrame extends NDframe {
       const dfValues = this.values;
       for (let i = 0; i < dfValues.length; i++) {
         const values = dfValues[i];
-        if (!values.includes(NaN)) {
+        if (!values.includes(NaN) && !values.includes(undefined) && !values.includes(null)) {
           newData.push(values);
           newIndex.push(this.index[i]);
         }
@@ -2100,8 +2100,9 @@ export default class DataFrame extends NDframe {
     });
 
     const sortedObjectArr = utils.sortObj(objToSort, ascending);
-    const sortedIndex = sortedObjectArr.map((obj) => obj.index);
+    let sortedIndex = sortedObjectArr.map((obj) => obj.index);
     const newData = sortedIndex.map((i) => (this.values)[i]);
+    sortedIndex = sortedIndex.map((i) => index[i]);
 
     if (inplace) {
       this.$setValues(newData);
diff --git a/danfojs-browser/src/core/series.js b/danfojs-browser/src/core/series.js
index 9e9cacb1..94e40313 100644
--- a/danfojs-browser/src/core/series.js
+++ b/danfojs-browser/src/core/series.js
@@ -789,9 +789,10 @@ export default class Series extends NDframe {
     if (inplace) {
       this.$setValues(data);
     } else {
-      const sf = this.copy();
-      sf.$setValues(data);
-      return sf;
+      return new Series(data, {
+        index: this.index,
+        config: { ...this.config }
+      });
     }
   }
 
diff --git a/danfojs-browser/tests/core/frame.js b/danfojs-browser/tests/core/frame.js
index 8e5f30c9..9bd09650 100644
--- a/danfojs-browser/tests/core/frame.js
+++ b/danfojs-browser/tests/core/frame.js
@@ -2047,6 +2047,17 @@ describe("DataFrame", function () {
       let rslt = [[2, 4, 6, 'c'], [0, 2, 4, 'b'], [360, 180, 360, 'a']];
       assert.deepEqual(df.values, rslt);
     });
+    it("sort index in descending order and retains index", function () {
+      let data = [[0, 2, 4, "b"],
+      [360, 180, 360, "a"],
+      [2, 4, 6, "c"]];
+
+      let df = new dfd.DataFrame(data, { "columns": ["col1", "col2", "col3", "col4"], index: ["b", "a", "c"] });
+      let df2 = df.sort_index({ ascending: false });
+      let rslt = ["c", "b", "a"];
+
+      assert.deepEqual(df2.index, rslt);
+    });
   });
 
   describe("append", function () {
diff --git a/danfojs-node/src/core/frame.js b/danfojs-node/src/core/frame.js
index 889e88c3..9a768eab 100644
--- a/danfojs-node/src/core/frame.js
+++ b/danfojs-node/src/core/frame.js
@@ -1239,7 +1239,7 @@ export default class DataFrame extends NDframe {
       const dfValues = this.values;
       for (let i = 0; i < dfValues.length; i++) {
         const values = dfValues[i];
-        if (!values.includes(NaN)) {
+        if (!values.includes(NaN) && !values.includes(undefined) && !values.includes(null)) {
           newData.push(values);
           newIndex.push(this.index[i]);
         }
@@ -2102,8 +2102,9 @@ export default class DataFrame extends NDframe {
     });
 
     const sortedObjectArr = utils.sortObj(objToSort, ascending);
-    const sortedIndex = sortedObjectArr.map((obj) => obj.index);
+    let sortedIndex = sortedObjectArr.map((obj) => obj.index);
     const newData = sortedIndex.map((i) => (this.values)[i]);
+    sortedIndex = sortedIndex.map((i) => index[i]);
 
     if (inplace) {
       this.$setValues(newData);
diff --git a/danfojs-node/src/core/series.js b/danfojs-node/src/core/series.js
index 09f3e88c..42555905 100644
--- a/danfojs-node/src/core/series.js
+++ b/danfojs-node/src/core/series.js
@@ -785,9 +785,10 @@ export default class Series extends NDframe {
     if (inplace) {
       this.$setValues(data);
     } else {
-      const sf = this.copy();
-      sf.$setValues(data);
-      return sf;
+      return new Series(data, {
+        index: this.index,
+        config: { ...this.config }
+      });
     }
   }
 
diff --git a/danfojs-node/tests/core/frame.js b/danfojs-node/tests/core/frame.js
index 463e4980..7e00dff2 100644
--- a/danfojs-node/tests/core/frame.js
+++ b/danfojs-node/tests/core/frame.js
@@ -644,7 +644,7 @@ describe("DataFrame", function () {
       let data = [[0, 2, 4], [360, 180, 360]];
       let df = new DataFrame(data, { columns: ["col1", "col2", "col3"] });
       assert.deepEqual(df.mean().values, [180, 91, 182]);
-      assert.deepEqual(df.mean().index, ["col1", "col2", "col3"] );
+      assert.deepEqual(df.mean().index, ["col1", "col2", "col3"]);
 
     });
     it("Return mean of a DataFrame along axis 0 (row)", function () {
@@ -1431,6 +1431,17 @@ describe("DataFrame", function () {
       assert.deepEqual(df.values, df_val);
 
     });
+    it("drop works for undefined values", function () {
+      let data = [[null, 1, 2, 3], [3, 4, undefined, 9], [5, 6, 7, 8]];
+      let column = ["A", "B", "C", "D"];
+      let df = new DataFrame(data, { columns: column });
+
+      let df_val = [[5, 6, 7, 8]];
+
+      df.dropna(0, { inplace: true });
+      assert.deepEqual(df.values, df_val);
+
+    });
   });
 
   describe("isna", function () {
@@ -2068,6 +2079,17 @@ describe("DataFrame", function () {
       let rslt = [[2, 4, 6, 'c'], [0, 2, 4, 'b'], [360, 180, 360, 'a']];
       assert.deepEqual(df.values, rslt);
     });
+    it("sort index in descending order and retains index", function () {
+      let data = [[0, 2, 4, "b"],
+      [360, 180, 360, "a"],
+      [2, 4, 6, "c"]];
+
+      let df = new DataFrame(data, { "columns": ["col1", "col2", "col3", "col4"], index: ["b", "a", "c"] });
+      let df2 = df.sort_index({ ascending: false });
+      let rslt = ["c", "b", "a"];
+
+      assert.deepEqual(df2.index, rslt);
+    });
   });
 
   describe("append", function () {