Javascript: how to match array and json?

Question

How can I find there is a match between an array and a json?

var fields = [ { public_name: 'hello', code_name: 'world' },
  { public_name: 'particles', code_name: 'pm2.5' },
  { public_name: 'humidity', code_name: 'hum' } ]

var species = [{"code_name":"hum","public_name":"humidity"},
  {"code_name":"pm2.5","public_name":"particles"},
  {"code_name":"world","public_name":"hello"}]


fields.forEach(function(field, index) {       
    if (field.code_name === species.code_name) {
        console.log('match:' + code_name)
    }
});

The result should be:

match: world
match: pm2.5
match: hum

Any ideas?

`if (field.code_name === species[index].code_name) { console.log('match:' + field.code_name) }` you need to iterate and compare with each value in `species`, use `Array#some` — Pranav C Balan, Jul 25 '16 at 07:33
Do you need to compare all properties for match or even if 1 property is matching, message should be shown — Rajesh, Jul 25 '16 at 07:36
You might like to look into something like [es5-shim](https://github.com/es-shims/es5-shim). It will give you access to lots of the new JavaScript features such as those used in the answers below. — David Gilbertson, Jul 25 '16 at 08:26

Nina Scholz · Accepted Answer · 2016-07-25T10:37:20.573

You could use a hash table for lookup.

var fields = [{ public_name: 'hello', code_name: 'world' }, { public_name: 'particles', code_name: 'pm2.5' }, { public_name: 'humidity', code_name: 'hum' }],
    species = [{ "code_name": "hum", "public_name": "humidity" }, { "code_name": "pm2.5", "public_name": "particles" }, { "code_name": "world", "public_name": "hello" }],
    match,
    hash = Object.create(null),
    getHashKey = function (o) { return o.public_name + '|' + o.code_name; };

fields.forEach(function (a) {
    hash[getHashKey(a)] = true;
});

match = fields.filter(function (a) {
    return hash[getHashKey(a)];
});

console.log(match);

Rajaprabhu Aravindasamy · Answer 2 · 2016-07-25T07:41:54.670

1

You can do it by using find() at this context,

fields.forEach(function(field, index) {       
   if(species.find((itm) => itm.code_name == field.code_name)) {
      console.log("match" , " : " , field.code_name)
   }
});

Or the better option would be using some() since it will return the result in Boolean's,

fields.forEach(function(field, index) {       
   if(species.some((itm) => itm.code_name == field.code_name)) {
      console.log("match" , " : " , field.code_name)
   }
});

edited Jul 25 '16 at 07:41

answered Jul 25 '16 at 07:34

Rajaprabhu Aravindasamy

66,513
17
101
130

Though I was going to do the same, do specify that `Array.find` has compatibility issues – Rajesh Jul 25 '16 at 07:35
1

@PranavCBalan Yeah, That would yield true/false unlike a find. find would return the matched element if any. – Rajaprabhu Aravindasamy Jul 25 '16 at 07:39
@Rajesh But eventually, browsers will start support ES6 shortly. So we have to start writing code in that. :) – Rajaprabhu Aravindasamy Jul 25 '16 at 07:43
@RajaprabhuAravindasamy but what about browsers like IE8 or IE9? At least you should mention it and if OP wants to use it for older browsers, he/she can add polyfill. – Rajesh Jul 25 '16 at 07:49

score 1 · Answer 3 · answered Jul 25 '16 at 07:44

1

If you can't use newer JS features, you can just nest two loops like so.

var fields = [
  { public_name: 'hello', code_name: 'world' },
  { public_name: 'hello', code_name: 'NO MATCH' },
  { public_name: 'particles', code_name: 'pm2.5' },
  { public_name: 'humidity', code_name: 'hum' }
];

var species = [
  {"code_name":"hum","public_name":"humidity"},
  {"code_name":"pm2.5","public_name":"particles"},
  {"code_name":"world","public_name":"hello"}
];

var matches = [];

fields.forEach(function(field, index) {
  species.forEach(function(spec) {
    if (spec.code_name === field.code_name) {
      matches.push(field.code_name);
    }
  });
});

document.getElementById('result').textContent = matches.join(', ');

<div id="result"></div>

answered Jul 25 '16 at 07:44

David Gilbertson

4,219
1
26
32

You should short-circuit loop on match. http://stackoverflow.com/questions/2641347/how-to-short-circuit-array-foreach-like-calling-break – Rajesh Jul 25 '16 at 07:51
Agreed, in theory. @teelou, if either array could grow bigger than a few thousand entries, you should consider performance and not continue looping after you have found a match. – David Gilbertson Jul 25 '16 at 07:55
for big arrays pre-hashing is much better – Variant Jul 25 '16 at 07:57

Javascript: how to match array and json?

3 Answers3