Dynamic nested for loops to be solved with recursi

Question

I'm trying to get a result looking something like this: Miniors | Boys | 54kg - 62kg where every value delimited by a pipe | comes from an array containing a certain "type of restriction". For example: ageGroups, genders, weightClasses (as seen above).

The way I'm able to get this result right now is if I hard code the nested forEach-loops (using underscorejs), but this means I have to now how many arrays I have to loop over to get wanted result. This works "fine":

var categories = [];
_.each(ageGroups, function(ageGroup) {
   _.each(gender, function(gender) {
     _.each(weightClasses, function(weightClass) {
       categories.push(ageGroup.name + ' | ' + gender.name + ' | ' + weightClass.name);
      });
   });
});

The output is an array (categories) with all the possible combinations of the restriction arrays.

Now, my problem is that I need a way to do the same with an unknown number of restriction arrays. My guess for a proper solution is recursion, BUT I haven't been able to produce anything that actually works since I'm not able to wrap my head around recursion just yet :)

A fiddle prepared with some test data can be found here: jsFiddle. The fiddle uses angular for some simple databinding and debugging the result output and underscorejs for handling the arrays.

Answer 1

I recently wrote a recursive function to create all combinations of arrays. You would have to translate your data into an array of arrays that my function uses, but that shouldn't be difficult.

Anyway, here's the code with a runnable example:

var v = [['Miniors','Kadettes','Juniors', 'Seniors'], ['Boys','Girls','Men','Women'],['54kg - 62kg','64kg - 70kg','71kg - 78kg','79kg - 84kg']];
var combos = createCombinations(v);
for(var i = 0; i < combos.length; i++) {
  document.getElementsByTagName("body")[0].innerHTML += combos[i] + "<br/>";
}

function createCombinations(fields, currentCombinations) {
  //prevent side-effects
  var tempFields = fields.slice();

  //recursively build a list combinations
  var delimiter = ' | ';
  if (!tempFields || tempFields.length == 0) {
    return currentCombinations;
  }
  else {
    var combinations = [];
    var field = tempFields.pop();

    for (var valueIndex = 0; valueIndex < field.length; valueIndex++) {
      var valueName = field[valueIndex];

      if (!currentCombinations || currentCombinations.length == 0) {
        var combinationName = valueName;
        combinations.push(combinationName);
      }
      else {
        for (var combinationIndex = 0; combinationIndex < currentCombinations.length; combinationIndex++) {
          var currentCombination = currentCombinations[combinationIndex];
          var combinationName = valueName + delimiter + currentCombination;
          combinations.push(combinationName);
        }
      }
    }
    return createCombinations(tempFields, combinations);
  }
}

Answer 2

function iterate(lists, fn)
{
  var values = [];
  function process(listIndex)
  {
    var list = lists[listIndex];

    // no list? create the value
    if (!list)
    {
      fn.apply(null, values);
      return;
    }

    for (var i = 0; i < list.length; i++)
    {
      values[listIndex] = list[i];
      process(listIndex+1);
    }
  }

  process(0);
}

here is a working example based on the data mentioned in your question: http://jsbin.com/boqucu/2/edit