How to access JSON array values without using index

Question

I have made a request to an API that is returning a JSON array like this:

My end goal is to take the attribute "State" and find all the "EventName" (s) where State: "PR" (or another state. I am getting the State input from a user dropdown) and put that into a list.

I know I can use the index (Ex: event_data[0].State returns "PR") to get the individual attributes but how can I avoid using the index to get all the State value (or EventName values) in the entire Array? Or is that even wise? I have tried the below, but it seemed to just grab all of the EventName values rather than just those for "PR". The expected output should be a list of event names for just "PR" like pr_list = ["Debby 2000", "Dean 2001", "Jeane 2004" ... "Maria 2017"];

pr_list = [];
for (i = 0; i < event_data.length; i++) {
  state_data = event_data[i].State;
  if (state_data = "PR") {
    console.log(event_data[i].EventName)
    pr_list.append(event_data[i].EventName);
  }
}

you're missing == in the if statement: if (state_data = "PR") - you're performing assignment, not comparison, thats why it takes all eventName and not just those with State equal to "PR" — Gibor
– Gibor, Commented Aug 20, 2019 at 13:56

MTCoster · Accepted Answer · 2019-08-20 13:56:01Z

2

You could use Array.filter() and Array.map() for this:

filtered_events = event_data.filter(event => (event.State === "PR"));
pr_list = filtered_events.map(event => event.EventName);

Regarding your existing code - you have a typo:

if (state_data = "PR") { ... }

should be:

if (state_data === "PR") { ... }

(more info on MDN)

answered Aug 20, 2019 at 13:56

MTCoster

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3 Comments

gwydion93 Over a year ago

This works great up front but I just want the EventName values in a list for "PR". pr_list = event_data.filter(event.EventName => (event.State === "PR")) doesn't quite work though.

MTCoster Over a year ago

@gwydion93 I noticed that after I posted my answer - it should do what you want now

gwydion93 Over a year ago

That works perfect! It was the filter that was the key.

LePirlouit · Accepted Answer · 2019-08-20 14:00:26Z

2

You could use Array.filter() and Array.map() for this:

pr_list = event_data.filter(event => (event.State === "PR")).map(event => event.EventName)

for unicity use a Set :

pr_list = [...new Set(event_data.filter(event => (event.State === "PR")).map(event => event.EventName))]

answered Aug 20, 2019 at 14:00

LePirlouit

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Comments

Neel Rathod · Accepted Answer · 2019-08-20 14:06:45Z

2

Native Way

const finalArray = [];
const event_data = [{ EventName: 'Event1', State: 'PR' }, { EventName: 'Event2', State: 'PQ' }];
for (i = 0; i < event_data.length; i += 1) {
  element = event_data[i];
  if (element.State === "PR") {
    finalArray.push(element.EventName);
  }
}
console.log(finalArray);

ES6 Way

const event_data = [{ EventName: 'Event1', State: 'PR' }, { EventName: 'Event2', State: 'PQ' }];
const finalArray = event_data.filter((f) => {
  return f.State &&
    f.State === 'PR';
}).map((m) => { return m.EventName; });
console.log(finalArray);

edited Aug 20, 2019 at 14:06

answered Aug 20, 2019 at 13:59

Neel Rathod

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Comments

Trần Công · Accepted Answer · 2019-08-20 14:20:24Z

2

You can using array.filter() function to get list have state is PR and array.map() function to get all eventId of list.

var array = [
  {eventId: '1', State: 'PR'},
  {eventId: '2', State: 'AR'},
  {eventId: '3', State: 'PR'}
];

// get all event with State is PR
array = array.filter(function (event) {
  return event.State === "PR";
});

// put all eventId in new array
var eventIds = array.map(function (event) {
   return event.eventId
});

console.log('eventIds:', eventIds);

answered Aug 20, 2019 at 14:20

Trần Công

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2 Comments

gwydion93 Over a year ago

I like this solution. I would use eventName instead but it may be useful to have a new array rather than just a list.

Trần Công Over a year ago

Ok, this is demo code so it is maybe not perfect. I'm happy to know that you like this solution.

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