Javascript remove row from multidimensional array when elements are duplicated

You can keep track of the already seen items in an object, and if you get an item which is not there in the seen, then push it to the result.

var seen = {};
var result = data.reduce(function(result, current) {
    if (!seen[current.HouseNo]) {
        seen[current.HouseNo] = true;
        result.push(current.HouseNo);
    }
    return result;
}, []);
console.log(result);

Output

[ 'firtree farm',
  'firtreefarm',
  'firtree farmhouse',
  'FirTree farmhouse' ]

If you want to maintain the object structure, then while pushing to the result, just create an object like this

result.push({HouseNo: current.HouseNo});

and the result would be

[ { HouseNo: 'firtree farm' },
  { HouseNo: 'firtreefarm' },
  { HouseNo: 'firtree farmhouse' },
  { HouseNo: 'FirTree farmhouse' } ]

If the Order of the data doesn't matter, then you can simply keep adding the HouseNo to an object and finally get the keys like this

var result = data.reduce(function(result, current) {
    result[current.HouseNo] = true;
    return result;
}, {});
console.log(Object.keys(result));