How to use Map.get() with array of arrays

Question

Is there any way to use Map.get() with an array of arrays (specifically in d3.js)?

Here's what I have: (1) Map – containing data in over 100 key-value pairs (2) Array of arrays – listing the keys of the data I want to pull from the Map for populating a table (only a subset of the 100+ values)

Here's what I need to create: (1) A new array of arrays – this new array should take each item from the first array in turn, look up the key in the Map and return the value.

I can get Map.get() to work just fine over a single array, but only if I specify the index of the nested array, like this:

var myMap;
var dataArray = [key_1, key_2, key_3, key_4, key_5, key_6]
var newArray = dataArray[0].map(function(d) {
              return myMap.get(d);
              });

But when my original array is an array of arrays, I can't figure out how to do it:

var myMap;
var dataArray = [
   [key_1, key_2, key_3],
   [key_4, key_5, key_6],
   [key_7, key_8, key_9]
   ]
var newArray = ???

Any suggestions?

T.J. Crowder · Accepted Answer · 2016-12-08 11:44:16Z

1

You have nested arrays, so use nested maps:

var newArray = dataArray.map(function(array) {
                   return array.map(function(d) {
                       return myMap.get(d);
                   });
               });

If creating functions in loops bothers you, you can split the recreated function out:

var newArray = dataArray.map(function(array) {
                   return array.map(mapOne);
               });
function mapOne(array) {
    return array.map(function(d) {
        return myMap.get(d);
    });
}

edited Dec 8, 2016 at 11:44

answered Dec 8, 2016 at 11:34

T.J. Crowder

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1 Comment

trf0412 Over a year ago

Thanks! Problem solved. I knew there had to be an elegant solution, but have very little experience with JavaScript.

Redu · Accepted Answer · 2016-12-08 11:52:39Z

0

Not only or 2D but for an indefinite ND array of keys you may also do as follows;

var myMap = new Map(),
dataArray = [["key_1", "key_2", ["key_31", "key_32", ["key_331"]]],
             ["key_4", "key_5", ["key_61", "key_62", ["key_631"]]],
             ["key_7", "key_8", ["key_91", "key_92", ["key_931"]]]
            ],
   getMap = (a,m) => a.map(k => Array.isArray(k) ? getMap(k,m) : m.get(k));
console.log(JSON.stringify(getMap(dataArray,myMap)));

answered Dec 8, 2016 at 11:52

Redu

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