use lodash javascript to full join two-dimensional array

Question

I have two two-dimensional array.

var arr1=[[1,20],[2,30]];
var arr2=[[2,40],[3,50]];

This is expected output:

[[1,20,null],[2,30,40],[3,null,50]]

It is like full join of two data frames. The logic is similar to this pseudo code:

df1.join(df2, df1[col_1] == df2[col_1], 'full')

but this case is for two-dimensional array. Can lodash do this? If not, how to do it in vanilla javascript?

Answer 1

Well, lodash can't do this, but we can:

function flatten2d(arr1, arr2) {
  const o1 = _.fromPairs(arr1);
  const o2 = _.fromPairs(arr2);
  const result = [];

  _.forEach(o1, (v, k) => {
    const v2 = o2[k] || null;
    result.push([k|0, v, v2]);
    delete o2[k];
  });

  // at this point, only items non-existing
  // in o1 are left in o2
  _.forEach(o2, (v, k) => {
    result.push([k|0, null, v]);
  });

  return result;
}

Testing:

flatten2d([[1,20],[2,30]], [[2,40],[3,50]])

Result:

[[1,20,null], [2,30,40], [3,null,50]]

Answer 2

If you don't have duplicate id's in any single array then you can try combine them, and group them using groupBy with first element (ie the key 0 ), and if you have duplicates, anyway I am not sure what exactly output you are looking for! Here is what you can do:

    _(arr1.concat(arr2)).groupBy('0').map(v=>
        [v[0][0]].concat(v.length > 1 ? v.map(m=>m[1]) : [v[0][1], null])
    ).value();

Here is an working snippet for you:

 var arr1=[[1,20],[2,30]]; var arr2=[[2,40],[3,50]]; var res = _(arr1.concat(arr2)).groupBy('0').map(v=> [v[0][0]].concat(v.length > 1 ? v.map(m=>m[1]) : [v[0][1],null]) ).value(); console.log(JSON.stringify(res)); 

 <script src="https://cdnjs.cloudflare.com/ajax/libs/lodash.js/4.17.4/lodash.js"></script>