Add backward support for query method

Author: risenW

danfojs-browser/package.json

@@ -35,7 +35,7 @@
     "build": "babel ./src -d ./dist --no-comments && yarn run bundle",
     "build:clean": "rimraf ./dist && rimraf ./lib && yarn run build",
     "lint": "eslint ./src",
-    "bundle": "webpack --mode development",
+    "bundle": "webpack --mode production",
     "coveralls": "cat ./coverage/lcov.info | ./node_modules/.bin/coveralls",
     "coverage": "nyc report --reporter=text-lcov | coveralls && nyc report --reporter=lcov",
     "patch": "npm version patch"

danfojs-browser/src/core/frame.js

@@ -2174,28 +2174,89 @@ export default class DataFrame extends NDframe {
 
   /**
      * Queries the DataFrame for rows that meet the boolean criteria.
-     * @param condition An array of boolean mask, one for each row in the DataFrame. Rows where the value are true will be returned.
-     * @param options.inplace Boolean indicating whether to perform the operation inplace or not. Defaults to false
+     * @param options
+     * - `column` A column name to query with.
+     * - `is` A logical operator. Can be one of the following: [">", "<", "<=", ">=", "==", "!="]
+     * - `to` A value to query with.
+     * - `condition` An array of boolean mask, one for each row in the DataFrame. Rows where the value are true will be returned.
+     *  If specified, then other parameters are ignored.
+     * - `inplace` Boolean indicating whether to perform the operation inplace or not. Defaults to false
     **/
-  query(condition, options) {
-    const { inplace } = { inplace: false, ...options };
+   query(options) {
+    const { inplace, condition, column, is, to } = { inplace: false, ...options };
+
+    if (condition) {
+      const result = _iloc({
+        ndFrame: this,
+        rows: condition
+      });
+
+      if (inplace) {
+        this.$setValues(result.values, false, false);
+        this.$setIndex(result.index);
+        return;
+      } else {
+        return result;
+      }
 
-    if (!condition) {
-      throw new Error("ParamError: condition must be specified");
     }
 
-    const result = _iloc({
-      ndFrame: this,
-      rows: condition
-    });
+    const operators = [">", "<", "<=", ">=", "==", "!="];
 
-    if (inplace) {
-      this.$setValues(result.values, false, false);
-      this.$setIndex(result.index);
+    let columnIndex, operator, value;
+
+    if (column) {
+      if (this.columns.includes(column)) {
+        columnIndex = this.columns.indexOf(column);
+      } else {
+        throw new Error(`ParamError: column ${column} not found in column names`);
+      }
+    } else {
+      throw new Error(`ParamError: specify a column name to query`);
+    }
+
+    if (is) {
+      if (operators.includes(is)) {
+        operator = is;
+      } else {
+        throw new Error(`ParamError: specified operato ${is} is not a supported. operator must be one of ${operators}`);
+      }
     } else {
-      return result;
+      throw new Error(`ParamError: specify an operator to apply. operator must be one of ${operators}`);
     }
 
+    if (to) {
+      value = to;
+    } else {
+      throw new Error("ParamError: specify a value to query by");
+    }
+
+    let data = this.values;
+    let index = this.index;
+    let newData = [];
+    let newIndex = [];
+
+    for (var i = 0; i < data.length; i++) {
+      let dataValue = data[i];
+      let elem = dataValue[columnIndex];
+      //use eval function for easy operation
+      //eval() takes in a string expression e.g eval('2>5')
+      if (eval(`elem${operator}value`)) {
+        newData.push(dataValue);
+        newIndex.push(index[i]);
+      }
+    }
+
+    if (inplace) {
+      this.$setValues(newData, false, false);
+      this.$setIndex(newIndex);
+      return;
+    } else {
+      return new DataFrame(newData, {
+        index: newIndex,
+        config: { ...this.config }
+      });
+    }
   }
 
   /**