Lodash retrieve index of the items from array of objects that have a boolean property equal to true

Question

I am a beginner with lodash i went from c# and i have used LINQ sometimes, i have learned that lodash can be used to do query linq style, but despite my attempts, cant able to get index of the items, from array of objects that have a boolean property equal to true in lodash. Can anyone help me?

My first try :

var indexofItemns =_.find( arrayOfItems, (item) => 
  (item.booleanProperty === true));

But, I have an array and i do:

var indexItems: number[] = [];
indexItems= _.times(
  arrayOfItems.length,
  _.find( arrayOfItems, (item) => (item.booleanProperty === true));

the second row does not compile neither.

Thanks

ben · Accepted Answer · 2018-09-24 10:27:39Z

2

You can achieve the same goal with pure JS. You don't need lodash

const data = [{
    booleanProperty: false
  },
  {
    booleanProperty: true
  },
  {
    booleanProperty: false
  },
  {
    booleanProperty: true
  },
  {
    booleanProperty: false
  }
];

const indexItems = data.map((item, index) => item.booleanProperty === true ? index : null).filter((item) => item !== null);


console.log(indexItems)

edited Sep 24, 2018 at 10:27

answered Sep 24, 2018 at 10:25

ben

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1 Comment

OliverRadini Over a year ago

You beat me to it, your answer is basically identical to mine so I've removed it

Koushik Chatterjee · Accepted Answer · 2018-09-24 11:46:24Z

1

If you need a single index satisfying that condition, you can use findIndex of es6 or lodash

data.findIndex(a=>a.booleanProperty)

If you need all the indexes satisfying your condition, you can either map and filter together sequentially (as shown in ben's answer) or you can merge them to a single reduce to iterate only once and build your index array. here we go:

data.reduce((r, a, i)=> (a.booleanProperty && r.push(i), r), [])

let data = [{"booleanProperty":false},{"booleanProperty":true},{"booleanProperty":false},{"booleanProperty":true},{"booleanProperty":false}];
    
let indexes = data.reduce((r, a, i)=> (a.booleanProperty && r.push(i), r), []);
  
  
console.log(indexes);

edited Sep 24, 2018 at 11:46

answered Sep 24, 2018 at 11:09

Koushik Chatterjee

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