Set variable to subset of array by condition in js

Question

I am relatively new to JS and would like to find the best method to set one variable equal to a subset of another variable another based on a dynamic condition.

In the example below,

clickedCode is a string that changes after each click event (all of the code below is within a click.event function).
features is an array of features with 400 elements, each containing a properties object which in turn contains elements such as latitude, longitude, etc.

cities is an empty array

      var clickedCode // dynamically changing string
      var cities = [];
      var features = map.queryRenderedFeatures({layers:['uni']});

for example, if I log some properties of the first feature, I will see:

var lon = features[0].properties.lon
var lat = features[0].properties.lat
var code = features[0].properties.code

console.log("" + lon + " " + lat + " " + code);

4.7005 50.8798 EMPHID

My objective is to subset features where features[i].properties.code is equal to clickedCode and then set cities equal to the resulting array so that roughly :

cities = features where features[i].properties.code === clickedCode

Any advice and explanation of structuring this in javascript would be helpful

GMaiolo · Accepted Answer · 2017-01-26 05:01:18Z

4

You could use Array.filter()

So in your case it would be something like this:

var cities = features.filter(function (feature){
    return feature.properties.code === clickedCode;
});

By simply passing a callback function to the filter (be sure that the function returns a truthy/falsy value, otherwise you could get undesired behavior).

answered Jan 26, 2017 at 5:01

GMaiolo

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Comments

Saman Hajizade · Accepted Answer · 2017-01-26 05:03:32Z

1

cities = features.filter(function(t)
         {
           return t.properties  &&  // check is not null
                  t.properties.code === clickedCode;
         });

the inner function runs for each element of array and returns a bool.

true => return element

false => filter it

answered Jan 26, 2017 at 5:03

Saman Hajizade

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Comments

Simone Sanfratello · Accepted Answer · 2017-01-26 07:43:44Z

0

You can create a dictionary using code as key (I suppose it's unique) Then access to the clickedCode by through the dictionary's key

var data = {}
features.each((feature) => {
  data[feature.properties.code] = properties
  cities.push(feature.properties.code)
})
console.log(data[clickedCode])

You also you don't need cities anymore, because

cities = Object.keys(data)

edited Jan 26, 2017 at 7:43

answered Jan 26, 2017 at 4:59

Simone Sanfratello

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2 Comments

iskandarblue Over a year ago

code is not unique - there are multiple elements in features with the same code as clickedCode = my goal is to filter only those and create an array out of them

Simone Sanfratello Over a year ago

so the @Goliadkin solution is the best

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