Compare two JSON object and find missing values using javascript

Question

I have two JSON objects counties, and ctyIndem. The counties object has all the counties in a US State, and ctyIndem has the indemnities paid in that State by county, but not those counties which no payment has been made. What I need to do is to iterate through both JSON, and if a county is missing from ctyIndem add the missing info from counties.

JS

var counties = [{
    FIPS: 1001,
    County: "Autauga",
    State: "ALABAMA"
    }, {
    FIPS: 1003,
    County: "Baldwin",
    State: "ALABAMA"
    }, {
   FIPS: 1005,
   County: "Barbour",
   State: "ALABAMA"
   }, {
   FIPS: 1007,
   County: "Bibb",
   State: "ALABAMA"
   }, {
   FIPS: 1009,
   County: "Blount",
   State: "ALABAMA"
   }, {
   FIPS: 1011,
  County: "Bullock",
  State: "ALABAMA"
  }];

  var ctyIndem = [{
  Year: 2015,
  State: "ALABAMA",
  id: 1001,
  County: "Autauga",
  Indem: 50
  }, {
  Year: 2015,
  State: "ALABAMA",
  id: 1003,
  County: "Baldwin",
  Indem: 200
  }, {
  Year: 2015,
  State: "ALABAMA",
  id: 1005,
  County: "Barbour ",
  Indem: 1501
  }];


  counties.forEach(function(a, v) {

  if (a.FIPS == ctyIndem[v].id) { //County is present, then is ok
    console.log(ctyIndem[v].id); 
   } else {//County not present, add new info

   var temp = [];
       temp.push({
       Year: ctyIndem[0].Year,
       State: a.State,
       id: a.FIPS,
       County: a.County,
       Indem: 0
      });
    Array.prototype.push.apply(ctyIndem, temp);
     }

     });

    console.log(ctyIndem);

The issue is when I iterate throught the array and gets to the point when the county FIPS and id don't match, I really not sure what to do there. I keep getting a Uncaught TypeError: Cannot read property 'id' of undefined error, because obviously there is no match. Thanks for any help.

It seems like your logic is all wrong. You're expecting the counties to have the same index in both arrays. You need to search the entire ctyIndem array to see if there's one with a matching ID. — Barmar
– Barmar, Commented Sep 23, 2016 at 23:43
Why are you using Array.prototype.push.apply? Just write ctyIndem.push({ ... }) — Barmar
– Barmar, Commented Sep 23, 2016 at 23:44

Barmar · Accepted Answer · 2016-09-23 23:50:44Z

1

Your searching logic is wrong. It only checks whether the element at the same index in ctyIndem has the matching id. But the indexes in the two arrays don't match. You need to search the entire array.

A simple way to do this is to create an object whose keys are the IDs you want to search for. Then you can just use a.FIPS as an index to see if it exists.

var ctyIds = {};
ctyIndem.forEach(function(c) {
    ctyIds[c.id] = true;
});

counties.forEach(function(a) {
    if (!ctyIds[a.FIPS]) {
        ctyIndem.push({
            Year: ctyIndem[0].Year,
            State: a.State,
            id: a.FIPS,
            County: a.County,
            Indem: 0
        });
    }
});

answered Sep 23, 2016 at 23:50

Barmar

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Comments

Charlie · Accepted Answer · 2016-09-23 22:33:43Z

1

In your loop you first need to check that ctyIndem[v] exists

//  v--- check that it exists
if (ctyIndem[v] && a.FIPS == ctyIndem[v].id) { //County is present, then is ok
  console.log(ctyIndem[v].id); 
 } else {//County not present, add new info

answered Sep 23, 2016 at 22:33

Charlie

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Comments

morecchia808 · Accepted Answer · 2016-09-24 00:14:24Z

1

First create a flat array with just the ids from ctyIndem. Using the Array.filter method, you can generate an array of counties missing from the list of ids. Then push in a new object for each missing county:

    var indemIds = ctyIndem.map(function (c) { return c.id });

    var missingFromIndem = counties.filter(function (cnty) {
      return indemIds.indexOf(cnty.FIPS) === -1;
    });

    missingFromIndem.forEach(function (cnty) {
      ctyIndem.push({
        id: cnty.FIPS,
        State: cnty.State,
        County: cnty.County
      });
    });

answered Sep 24, 2016 at 0:14

morecchia808

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