Lodash: Remove consecutive duplicates from an array

Question

I need to reduce this array of objects

[
  {id:1, value:'A'},
  {id:2, value:'B'},
  {id:3, value:'B'},
  {id:4, value:'B'},
  {id:5, value:'A'},
  {id:6, value:'A'},
  {id:7, value:'B'}
]

to

[
  {id:1, value:'A'},
  {id:2, value:'B'},
  {id:5, value:'A'},
  {id:7, value:'B'}
]

If consecutive objects have the same value, it keeps the first one and removes the rest.

My current solution is

var lastValue = undefined;
var result = [];
var propPath = 'value'; // I need later to reference nested props

objects.filter(function(object){
  var value = _.at(object, propPath);
  if (!_.isEqual(value, lastValue)){
    result.push(object);
    lastValue = value;
  }
});

console.log(result);

My questions is, as Lodash has a lot of features, is there a Lodash way of doing this more simply? Maybe some pre-built solution without using helper variables (lastValue and result).

GG. · Accepted Answer · 2016-04-25 21:43:00Z

4

This can be solved with .reject:

_.reject(objects, function (object, i) {
    return i > 0 && objects[i - 1].value === object.value;
});

DEMO

answered Apr 25, 2016 at 21:43

GG.

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2 Comments

mr.Kame Over a year ago

This is exactly what I need, but the lodash documentation says nothing about the second argument (index) of the predicate. Is the document outdated or is this something unofficial, internal, or subject to change?

GG. Over a year ago

All the methods to manipulate collections have a predicate with three arguments: (value, index|key, collection). I guess it's just missing in _.reject documentation but the other ones have this detail (_.filter, _.map, _.forEach, _.every, _.some, etc). For info, the third argument collection is useful in some case, e.g. _.filter(_.sortBy(items, 'id'), function (item, i, sortedItems) { … }.

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