Removing duplicate objects with Underscore for Javascript

by

.uniq/.unique accepts a callback

var list = [{a:1,b:5},{a:1,c:5},{a:2},{a:3},{a:4},{a:3},{a:2}];

var uniqueList = _.uniq(list, function(item, key, a) { 
    return item.a;
});

// uniqueList = [Object {a=1, b=5}, Object {a=2}, Object {a=3}, Object {a=4}]

Notes:

  1. Callback return value used for comparison
  2. First comparison object with unique return value used as unique
  3. underscorejs.org demonstrates no callback usage
  4. lodash.com shows usage

Another example :
using the callback to extract car makes, colors from a list

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