lodash.js fiddle

Added lodash from cdnjs.com in order to have lodash capabilities in chrome.

HTML

<script src="//cdnjs.cloudflare.com/ajax/libs/lodash.js/1.2.1/lodash.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/lodash.js/4.17.10/lodash.min.js"></script>

JavaScript

function merge(array) {
  return _.uniqWith(array, compareAndMerge)
}

function compareAndMerge(first, second) {
    if (first.field === second.field) {
        first.values = second.values = [].concat(first.values, second.values)
        return true
    }
    return false
}


var data = [{
  field: 'Currency',
  operator: 'IN',
  values: ['usd']
}, {
  field: 'Currency',
  operator: 'IN',
  values: ['gbp']
}, {
  field: 'Amount',
  operator: 'IN',
  values: [2]
},
{
  field: 'Amount',
  operator: 'IN',
  values: [3]
}]

console.log(merge(data))