How to use underscore.js to produce a flatten result

Question

The json object is

var data = [{\"Parent\":1,\"Child\":[4,5,6]},{\"Parent\":2},{\"Parent\":3}]

How can I use underscore.js chain/map/pluck

Answer 1

If you want to use underScore.js to flatten an array of many arrays into one array of elements, that's how you do it. Follow my example:

My graph has 2 series. Each series has a name and a sequence of datapoints {xtime, yValue}. My goal is to iron out all the data points from 2 series into one series of data points so to fill out a table.

var reducedArray = // flatten an array of series of data-objects into one series of data-objects
_.flatten( _.map( AllMySeries, function ( aSeries ) {
    return ( _.map( aSeries.dataPoints, function ( aPoint ) {
                return { curveID: aSeries.legendText, xT: aPoint.x, yVal: aPoint.y };
            } ) );
} ) );

My result :

'Series1','2017-04-19 08:54:19',1
'Series1','2017-04-19 08:59:19',0
'Series1','2017-04-19 09:04:19',1
'Series2','2017-04-19 08:54:19',1
'Series2','2017-04-19 08:59:19',0
'Series2','2017-04-19 09:04:19',1  

Answer 2

Assuming you want to first get the parents and then get the children:

_.chain(data).pluck("Parent")
             .concat(_.flatten(_(data).pluck("Child")))
             .reject(_.isUndefined)
             .value()

Answer 3

Here's a shorter solution:

flat = _.flatten(_.map(data, _.values)) 

Answer 4

Alternatively, if you want a function that can universally flatten any collection of objects or arrays,

You could extend Underscore with:

_.mixin({crush: function(l, s, r) {return _.isObject(l)? (r = function(l) {return _.isObject(l)? _.flatten(_.map(l, s? _.identity:r)):l;})(l):[];}});

Crush (for lack of a better name) can be called like _.crush(list, [shallow]) or _(list).crush([shallow]) and behaves exactly like a generalized form of Underscore's built-in Flatten.

It can be passed a collection of nested objects, arrays, or both of any depth and will return a single-leveled array containing all of the input's values and own properties. Like Flatten, if it is passed an additional argument which evaluates to true, a "shallow" execution is performed with the output only flattened one level.

Example 1:

_.crush({
   a: 1,
   b: [2],
   c: [3, {
      d: {
         e: 4
      }
   }]
});

//=> [1, 2, 3, 4]

Example 2:

_.crush({
   a: 1,
   b: [2],
   c: [3, {
      d: {
         e: 4
      }
   }]
}, true);

//=> [1, 2, 3, {
//      d: {
//         e: 4
//      }
//   }]

---

An explanation of the code itself is as follows:

_.mixin({  // This extends Underscore's native object.

  crush: function(list, shallow, r) {  // The "r" is really just a fancy
                                       // way of declaring an extra variable
                                       // within the function without
                                       // taking up another line.

    return _.isObject(list)?  // Arrays (being a type of object)
                              // actually pass this test too.

      (r = function(list) {  // It doesn't matter that "r" might have
                             // been passed as an argument before,
                             // as it gets rewritten here anyway.

        return _.isObject(list)?  // While this test may seem redundant at
                                  // first, because it is enclosed in "r",
                                  // it will be useful for recursion later.

          _.flatten(_.map(list, shallow?  // Underscore's .map is different
                                          // from plain Javascript's in
          // _.map will always return     // that it will apply the passed
          // an array, which is why we    // function to an object's values
          // can then use _.flatten.      // as well as those of an array.

            _.identity  // If "shallow" is truthy, .map uses the identity
                        // function so "list" isn't altered any further.

            : r  // Otherwise, the function calls itself on each value.
          ))
          : list  // The input is returned unchanged if it has no children.
        ;
      })(list)  // The function is both defined as "r" and executed at once.

      : []  // An empty array is returned if the initial input
    ;       // was something other than an object or array.
  }
});

Hope it helps if anyone needs it. :)