Variable replacement in string from given json

Question

Hi guys need some help with this issue, i have one formula string (PerilRateP001_0+PerilRateP002_1+PerilRateP003_2+PerilRateP004_3)*SumInsured*1*(0.01) and also i have given json

scope {
  BasicRate: '0.0512',
  PerilRate: [ { 'Perils Code': 'AIRCRAFT DAMAGE', 'Basis Indicator': 'P' } ],
  ClauseRate: [
    {
      ClauseCode: 'SMOKE DAMAGE',
      'Basis Indicator': 'P',
      ApplyTo: 'F&L'
    }
  ],
  'Questionnaire 1': [ { QuestLoading1: 'Yes' } ],
  SumInsured: '100000',
  ClauseFactorRate: '0.002925',
  PerilRateP001_0: '0.0060',
  ClauseRateC022_0: '10.0000',
  Loading: '10',
  productId: 'FNL0001',
  BasicPremium1: 51.2
}

now what i want to do is i want to substitute value of variables in formula string from given json.the json does not have all the variables present in the formula string so what i want to do is if the variable is associated with + or - sign substitute it with 0 and if the variable is associated with * or / sign then substitute it with 1. Any idea how can i achieve it. Have been struggling with it from 2 days and still unable to figure out the solution any help is greatly appreciated

The most resilient solution would be an expression parser, particularly if you need to then evaluate it (avoiding `eval`). — Dave Newton, Mar 03 '20 at 17:45
@DaveNewton i am using math.js library and have access to methods like evaluate and parse but i am not sure how to use parse in correct way. Will parse function be sufficient for solving the above problem? — , Mar 03 '20 at 17:50
@str what i have posted here is what appears in my console. The actual data is json only — , Mar 03 '20 at 17:52
Is it always the same equation ? Or at least always the same variables in the equation ? — François Huppé, Mar 03 '20 at 17:52
@FrançoisHuppé no its just one of the dynamic formulas that will get generated in the insurance application i am working on. All the formulas are dynamic and the json is also dynamic — , Mar 03 '20 at 18:01

score 0 · Answer 1 · answered Mar 03 '20 at 18:39

Using math.js, here is how you could do:

var data = {
  BasicRate: '0.0512',
  PerilRate: [ { 'Perils Code': 'AIRCRAFT DAMAGE', 'Basis Indicator': 'P' } ],
  ClauseRate: [
    {
      ClauseCode: 'SMOKE DAMAGE',
      'Basis Indicator': 'P',
      ApplyTo: 'F&L'
    }
  ],
  'Questionnaire 1': [ { QuestLoading1: 'Yes' } ],
  SumInsured: '100000',
  ClauseFactorRate: '0.002925',
  PerilRateP001_0: '0.0060',
  ClauseRateC022_0: '10.0000',
  Loading: '10',
  productId: 'FNL0001',
  BasicPremium1: 51.2
};

var formula = '(PerilRateP001_0+PerilRateP002_1+PerilRateP003_2+PerilRateP004_3)*SumInsured*1*(0.01)';

// parse formula into an expression tree
var formulaTree = math.parse(formula);

// use filter to find variables present in the formula
var variables = formulaTree.filter(function (node) {
    // check if node is a variable
    if(node.isSymbolNode){ 
        // check if variable is in data array   
        if(data[node.name]){  
            formula = formula.replace(node.name, data[node.name]);
        }
        else{
            // replace missing variable with 0
            formula = formula.replace(node.name, 0);

            // fix product and division by 0
            formula = formula.replace('*0', '*1');
            formula = formula.replace('/0', '/1'); 
        }
    }
});

console.log(formula);
console.log(math.evaluate(formula));

<script src="https://cdnjs.cloudflare.com/ajax/libs/mathjs/6.6.1/math.js"></script>

That's a lot of work for something MathJS already does. Completely removing variables is nice for debugging, but useless for math. — Dave Newton, Mar 03 '20 at 18:40
But the problem is to find and replace the formula's unknown variables by ones or zeros. I'm not sure math.js evaluate method can directly do this.... — François Huppé, Mar 03 '20 at 18:51
No, it won't--you're right, I missed the info at the bottom of the question. Parsing is the answer. — Dave Newton, Mar 03 '20 at 19:24

Variable replacement in string from given json

1 Answers1