simplify init

lib/helpers.js

@@ -74,5 +74,5 @@ export const flatten = (arr) => {
 };
 
 export const removeSymbols = string => {
-  return string.replace(/\W/g, '');
+  return string.toString().replace(/\W/g, '');
 };

lib/index.js

@@ -30,6 +30,7 @@ let Equation = {
 
     return stack;
   },
+
   /**
     * Creates an equation function which replaces variables
     * in the given expression with the values specified in order,
@@ -49,9 +50,7 @@ let Equation = {
     let variables = [];
 
     stack.forEach(a => {
-      if (typeof a === 'string' && !_.isNumber(a) &&
-          !operators[a] && a === a.toLowerCase()) {
-        // grouped variables like (y) need to have their parantheses removed
+      if (isVariable(a)) {
         variables.push(_.removeSymbols(a));
       }
     });
@@ -69,6 +68,31 @@ let Equation = {
     };
   },
 
+  /**
+    * Simplifies a math expression
+    *
+    * Example:
+    *   2*x^2 + x - 2*x - x^2
+    *   becomes
+    *   x^2 - x
+    *
+    * @param {String} expression
+    *        The expression to create an equation for (containing variables)
+    * @return {String}
+    *         The simplified expression
+    */
+  simplify(expression) {
+    let stack = parseExpression(expression);
+    stack = sortStack(stack);
+    stack = _.parseNumbers(stack);
+
+    console.dir(stack, {
+      depth: null
+    });
+
+    return expression;
+  },
+
   registerOperator(key, options) {
     operators[key] = options;
   },
@@ -142,6 +166,12 @@ const parseExpression = expression => {
   return parseGroups(stack);
 };
 
+const isVariable = char => {
+  let ch = _.removeSymbols(char);
+  return typeof ch === 'string' && !_.isNumber(ch) &&
+         !operators[ch] && char === ch.toLowerCase();
+};
+
 /**
   * Takes the parsed array from parseExpression and
   * groups up expressions in parantheses in deep arrays